diff --git a/custom_components/nestquest/binary_sensor.py b/custom_components/nestquest/binary_sensor.py
new file mode 100644
index 0000000..7cd45b3
--- /dev/null
+++ b/custom_components/nestquest/binary_sensor.py
@@ -0,0 +1,191 @@
+"""Per-child binary sensors (Feature 10, task 4).
+
+Two binary sensors per active child, both reading only the coordinator
+snapshot (the same ChildDaySnapshot the day sensors read):
+
+- ``binary_sensor.nestquest_<child>_all_done`` — ON exactly when the
+  child owes quests today (due today > 0) AND owes none of them any
+  more (remaining today == 0).  A zero-quest day is OFF: the
+  celebration automation must never fire on an empty day (the
+  day-complete event carries the same rule, Feature 10 task 7).
+- ``binary_sensor.nestquest_<child>_present_today`` — ON when the
+  presence engine resolves the child present on the HA-local date
+  (schedules and overrides, D-004 anchor-date arithmetic).
+
+Naming and registry identity follow the day sensors' contract: names
+slug to the documented entity_id shape; unique_ids are built from the
+child's database id, never the display name, so a rename never
+orphans an entity's history.
+"""
+from __future__ import annotations
+
+from collections.abc import Callable, Iterable
+from typing import Any
+
+from homeassistant.components.binary_sensor import BinarySensorEntity
+from homeassistant.config_entries import ConfigEntry
+from homeassistant.core import HomeAssistant
+from homeassistant.helpers.entity import DeviceInfo
+from homeassistant.helpers.update_coordinator import CoordinatorEntity
+
+from .const import DOMAIN
+from .coordinator import ChildDaySnapshot, NestQuestCoordinator
+
+
+class _NestQuestChildBinarySensor(CoordinatorEntity, BinarySensorEntity):
+    """Base for the per-child binary sensors.
+
+    Registry identity is built from the child's database id and never
+    changes; the displayed name and device label re-derive from the
+    child's CURRENT snapshot on every read, so a rename propagates on
+    the next refresh without orphaning history.  A child absent from
+    the latest snapshot (a deactivation; removal is a later task's
+    scope) yields ``None`` states rather than stale values.
+    """
+
+    _name_suffix: str = ""
+
+    def __init__(
+        self,
+        coordinator: NestQuestCoordinator,
+        child: ChildDaySnapshot,
+    ) -> None:
+        super().__init__(coordinator)
+        self._child_id = child.child_id
+        self._fallback_name = child.child_name
+
+    @property
+    def _child(self) -> ChildDaySnapshot | None:
+        """Return the child's current day snapshot, or None."""
+        data = self.coordinator.data
+        if data is None:
+            return None
+        for child in data.children:
+            if child.child_id == self._child_id:
+                return child
+        return None
+
+    def _displayed_child_name(self) -> str:
+        child = self._child
+        return child.child_name if child is not None else self._fallback_name
+
+    @property
+    def name(self) -> str | None:
+        return f"NestQuest {self._displayed_child_name()} {self._name_suffix}"
+
+    @property
+    def device_info(self) -> DeviceInfo:
+        return DeviceInfo(
+            identifiers={(DOMAIN, f"child_{self._child_id}")},
+            name=f"NestQuest {self._displayed_child_name()}",
+            manufacturer="NestQuest",
+        )
+
+    @property
+    def extra_state_attributes(self) -> dict[str, Any] | None:
+        child = self._child
+        if child is None:
+            return None
+        return {
+            "child_id": child.child_id,
+            "child_name": child.child_name,
+        }
+
+
+class NestQuestAllDoneSensor(_NestQuestChildBinarySensor):
+    """ON when the child had quests today and owes none of them."""
+
+    _name_suffix = "all done"
+
+    def __init__(
+        self,
+        coordinator: NestQuestCoordinator,
+        child: ChildDaySnapshot,
+    ) -> None:
+        super().__init__(coordinator, child)
+        self._attr_unique_id = f"{DOMAIN}_child_{child.child_id}_all_done"
+
+    @property
+    def is_on(self) -> bool | None:
+        child = self._child
+        if child is None:
+            return None
+        # Zero-quest days are OFF, not ON: an empty day must never fire
+        # the celebration automation.
+        return child.due_today > 0 and child.remaining_today == 0
+
+
+class NestQuestPresentTodaySensor(_NestQuestChildBinarySensor):
+    """ON when the child is at this house today (presence engine)."""
+
+    _name_suffix = "present today"
+
+    def __init__(
+        self,
+        coordinator: NestQuestCoordinator,
+        child: ChildDaySnapshot,
+    ) -> None:
+        super().__init__(coordinator, child)
+        self._attr_unique_id = f"{DOMAIN}_child_{child.child_id}_present_today"
+
+    @property
+    def is_on(self) -> bool | None:
+        child = self._child
+        if child is None:
+            return None
+        return child.present
+
+
+def _child_binary_sensors(
+    coordinator: NestQuestCoordinator, child: ChildDaySnapshot
+) -> tuple[_NestQuestChildBinarySensor, ...]:
+    """Build the two documented binary sensors for one active child."""
+    return (
+        NestQuestAllDoneSensor(coordinator, child),
+        NestQuestPresentTodaySensor(coordinator, child),
+    )
+
+
+async def async_setup_entry(
+    hass: HomeAssistant,
+    entry: ConfigEntry,
+    async_add_entities: Callable[..., None],
+) -> None:
+    """Create the two binary sensors per active child.
+
+    Entities are created for the snapshot's children at platform
+    setup; a coordinator listener adds sensors for children that first
+    appear on a later refresh (the day sensors' same pattern, so a new
+    child's whole entity set lands together).  Deactivated children
+    are NOT removed here — removal is a later task's scope.
+    """
+    coordinator = entry.runtime_data.coordinator
+    known_child_ids: set[int] = set()
+
+    def _add_new_children(children: Iterable[ChildDaySnapshot]) -> None:
+        new_children = [
+            child
+            for child in children
+            if child.child_id not in known_child_ids
+        ]
+        if not new_children:
+            return
+        known_child_ids.update(child.child_id for child in new_children)
+        async_add_entities(
+            [
+                sensor
+                for child in new_children
+                for sensor in _child_binary_sensors(coordinator, child)
+            ]
+        )
+
+    data = coordinator.data
+    if data is not None:
+        _add_new_children(data.children)
+
+    def _handle_coordinator_update() -> None:
+        data = coordinator.data
+        if data is not None:
+            _add_new_children(data.children)
+
+    coordinator.async_add_listener(_handle_coordinator_update)
diff --git a/custom_components/nestquest/const.py b/custom_components/nestquest/const.py
index 82ef273..3d1d89a 100644
--- a/custom_components/nestquest/const.py
+++ b/custom_components/nestquest/const.py
@@ -8,8 +8,8 @@ LOGGER_NAME = "custom_components.nestquest"
 LOGGER = logging.getLogger(LOGGER_NAME)
 
 # Platforms set up per config entry (Feature 10): the per-child day
-# sensors. binary_sensor joins when task 4's entities land.
-PLATFORMS: list[str] = ["sensor"]
+# sensors and binary sensors.
+PLATFORMS: list[str] = ["sensor", "binary_sensor"]
 
 #: Canonical domain-global service names (design/ENTITIES-AND-SERVICES.md §2
 #: plus the existing Feature 07 regenerate service).
diff --git a/tests/test_binary_sensors.py b/tests/test_binary_sensors.py
new file mode 100644
index 0000000..2c31abf
--- /dev/null
+++ b/tests/test_binary_sensors.py
@@ -0,0 +1,134 @@
+"""Tests for the per-child binary sensors (Feature 10, task 4)."""
+from __future__ import annotations
+
+import datetime
+
+from conftest import wire_entry_to_registry
+
+from custom_components.nestquest import async_setup_entry
+from custom_components.nestquest.children import create_child
+from custom_components.nestquest.const import DOMAIN
+from custom_components.nestquest.dao_presence import PresenceSchedulesDao
+from custom_components.nestquest.materialize import materialize
+from custom_components.nestquest.quest_definitions import (
+    create_quest_definition,
+)
+from custom_components.nestquest.recurrence import ScheduleRule
+from custom_components.nestquest.completion import complete_instance
+
+SEED_HORIZON_DAYS = 3
+
+
+def _binary(hass, child_id: int, kind: str):
+    return hass.entities[f"{DOMAIN}_child_{child_id}_{kind}"]
+
+
+async def _setup_entry(hass, make_entry):
+    entry = wire_entry_to_registry(make_entry(), hass.registry)
+    assert await async_setup_entry(hass, entry) is True
+    return entry
+
+
+async def _seed_two_children(database) -> tuple:
+    ada = await create_child(database, "Ada")
+    bo = await create_child(database, "Bo")
+    today = datetime.date.today()
+    await create_quest_definition(
+        database,
+        "Brush teeth",
+        ScheduleRule.from_dict(
+            {"rule_type": "daily", "start_date": today.isoformat()}
+        ),
+        [ada.id, bo.id],
+        ["morning"],
+    )
+    end = (today + datetime.timedelta(days=SEED_HORIZON_DAYS)).isoformat()
+    await materialize(database, today.isoformat(), end, today=today)
+    return ada, bo
+
+
+async def test_all_done_off_with_open_quests_and_zero_quests(
+    hass, make_entry
+) -> None:
+    """all_done is OFF while quests are owed AND on a zero-quest day;
+    a child with no quests never fires the celebration automation."""
+    entry = await _setup_entry(hass, make_entry)
+    coordinator = entry.runtime_data.coordinator
+    database = entry.runtime_data.database
+    ada, _bo = await _seed_two_children(database)
+    await create_child(database, "Cory")  # zero quests
+    await coordinator.async_refresh()
+
+    assert _binary(hass, ada.id, "all_done").is_on is False
+    cory = [
+        child for child in coordinator.data.children
+        if child.child_name == "Cory"
+    ][0]
+    assert _binary(hass, cory.child_id, "all_done").is_on is False
+
+
+async def test_all_done_on_only_when_day_clear(hass, make_entry) -> None:
+    entry = await _setup_entry(hass, make_entry)
+    coordinator = entry.runtime_data.coordinator
+    database = entry.runtime_data.database
+    ada, _bo = await _seed_two_children(database)
+    await coordinator.async_refresh()
+    snapshot_ada = [
+        child for child in coordinator.data.children
+        if child.child_id == ada.id
+    ][0]
+    instance_id = snapshot_ada.instances[0].instance_id
+    await complete_instance(
+        database,
+        instance_id,
+        actor_source="panel",
+        actor_child_id=ada.id,
+    )
+    await coordinator.async_refresh()
+    assert _binary(hass, ada.id, "all_done").is_on is True
+
+
+async def test_present_today_on_without_schedule_off_when_absent(
+    hass, make_entry
+) -> None:
+    """No schedule means present every day; an all-absent pattern
+    today reports OFF."""
+    entry = await _setup_entry(hass, make_entry)
+    coordinator = entry.runtime_data.coordinator
+    database = entry.runtime_data.database
+    ada, _bo = await _seed_two_children(database)
+    await create_child(database, "Cory")
+    today = datetime.date.today()
+    await coordinator.async_refresh()
+    cory = [
+        child for child in coordinator.data.children
+        if child.child_name == "Cory"
+    ][0]
+    await PresenceSchedulesDao(database).upsert_by_child(
+        cory.child_id, 1, today.isoformat(), ""
+    )
+    await coordinator.async_refresh()
+
+    assert _binary(hass, ada.id, "present_today").is_on is True
+    assert _binary(hass, cory.child_id, "present_today").is_on is False
+
+
+async def test_binary_sensor_identity_and_attributes(hass, make_entry) -> None:
+    entry = await _setup_entry(hass, make_entry)
+    coordinator = entry.runtime_data.coordinator
+    database = entry.runtime_data.database
+    ada, _bo = await _seed_two_children(database)
+    await coordinator.async_refresh()
+
+    all_done = _binary(hass, ada.id, "all_done")
+    present = _binary(hass, ada.id, "present_today")
+    assert all_done.unique_id == f"nestquest_child_{ada.id}_all_done"
+    assert present.unique_id == f"nestquest_child_{ada.id}_present_today"
+    assert all_done.name == "NestQuest Ada all done"
+    assert present.name == "NestQuest Ada present today"
+    for entity in (all_done, present):
+        assert entity.device_info.name == "NestQuest Ada"
+        assert entity.extra_state_attributes == {
+            "child_id": ada.id,
+            "child_name": "Ada",
+        }
diff --git a/tests/test_const.py b/tests/test_const.py
index dc9e255..361ca83 100644
--- a/tests/test_const.py
+++ b/tests/test_const.py
@@ -28,10 +28,10 @@ def test_logger() -> None:
 
 
 def test_platforms() -> None:
-    """Verify PLATFORMS is defined as the sensor platform list."""
+    """Verify PLATFORMS is defined as the sensor + binary_sensor list."""
     assert hasattr(const, "PLATFORMS")
     assert isinstance(const.PLATFORMS, list)
-    assert const.PLATFORMS == ["sensor"]
+    assert const.PLATFORMS == ["sensor", "binary_sensor"]
 
 
 def test_sqlite_db_filename() -> None:
diff --git a/tests/test_sensors.py b/tests/test_sensors.py
index cf0478b..14cd27b 100644
--- a/tests/test_sensors.py
+++ b/tests/test_sensors.py
@@ -104,13 +104,16 @@ async def test_every_active_child_gets_five_sensors_with_documented_identity(
         hass, make_entry
     )
     database = entry.runtime_data.database
-    assert hass.config_entries.forwarded_platforms == ["sensor"]
+    assert hass.config_entries.forwarded_platforms == [
+        "sensor",
+        "binary_sensor",
+    ]
     await _complete_first_instance(database, coordinator, ada)
     await coordinator.async_refresh()
 
     # Two quest children plus the zero-quest child: three children x
-    # five sensors, no duplicates.
-    assert len(hass.entities) == 15
+    # (five sensors + two binary sensors), no duplicates.
+    assert len(hass.entities) == 21
     expected = {
         ada.id: ("Ada", 1, 1, 0, 100),
         bo.id: ("Bo", 1, 0, 1, 0),
@@ -324,7 +327,7 @@ async def test_repeated_refreshes_do_not_duplicate_entities(
     )
     await coordinator.async_refresh()
     await coordinator.async_refresh()
-    assert len(hass.entities) == 15
+    assert len(hass.entities) == 21
 
 
 async def test_setup_with_no_children_registers_no_entities(
@@ -339,7 +342,10 @@ async def test_unload_unloads_platforms(hass, make_entry) -> None:
     entry = wire_entry_to_registry(make_entry(), hass.registry)
     assert await async_setup_entry(hass, entry) is True
     assert await async_unload_entry(hass, entry) is True
-    assert hass.config_entries.unloaded_platforms == ["sensor"]
+    assert hass.config_entries.unloaded_platforms == [
+        "sensor",
+        "binary_sensor",
+    ]
 
 
 async def test_rename_propagates_to_name_and_device_label(