diff --git a/crates/xy-supervisor/src/child.rs b/crates/xy-supervisor/src/child.rs
new file mode 100644
index 0000000..fd9cc15
--- /dev/null
+++ b/crates/xy-supervisor/src/child.rs
@@ -0,0 +1,92 @@
+use std::sync::Arc;
+use tokio::sync::{Mutex, oneshot};
+
+#[async_trait::async_trait]
+pub trait ChildHandle: Send + 'static {
+    fn pid(&self) -> u32;
+    async fn wait(&mut self) -> std::io::Result<Option<i32>>;
+    fn terminate(&mut self) -> std::io::Result<()>;
+    fn kill(&mut self) -> std::io::Result<()>;
+}
+
+pub struct MockChild {
+    pid: u32,
+    exit_rx: Arc<Mutex<oneshot::Receiver<Option<i32>>>>,
+    terminate_tx: Option<oneshot::Sender<()>>,
+    kill_tx: Option<oneshot::Sender<()>>,
+}
+
+pub struct MockChildController {
+    pub exit_tx: Option<oneshot::Sender<Option<i32>>>,
+    pub terminate_rx: oneshot::Receiver<()>,
+    pub kill_rx: oneshot::Receiver<()>,
+}
+
+impl MockChild {
+    pub fn new(pid: u32) -> (Self, MockChildController) {
+        let (exit_tx, exit_rx) = oneshot::channel();
+        let (terminate_tx, terminate_rx) = oneshot::channel();
+        let (kill_tx, kill_rx) = oneshot::channel();
+        let child = Self {
+            pid,
+            exit_rx: Arc::new(Mutex::new(exit_rx)),
+            terminate_tx: Some(terminate_tx),
+            kill_tx: Some(kill_tx),
+        };
+        let ctl = MockChildController {
+            exit_tx: Some(exit_tx),
+            terminate_rx,
+            kill_rx,
+        };
+        (child, ctl)
+    }
+}
+
+#[async_trait::async_trait]
+impl ChildHandle for MockChild {
+    fn pid(&self) -> u32 {
+        self.pid
+    }
+
+    async fn wait(&mut self) -> std::io::Result<Option<i32>> {
+        let mut rx = self.exit_rx.lock().await;
+        match (&mut *rx).await {
+            Ok(code) => Ok(code),
+            Err(_) => Err(std::io::Error::other("exit_tx dropped")),
+        }
+    }
+
+    fn terminate(&mut self) -> std::io::Result<()> {
+        if let Some(tx) = self.terminate_tx.take() {
+            let _ = tx.send(());
+        }
+        Ok(())
+    }
+
+    fn kill(&mut self) -> std::io::Result<()> {
+        if let Some(tx) = self.kill_tx.take() {
+            let _ = tx.send(());
+        }
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[tokio::test]
+    async fn mock_child_exit() {
+        let (mut child, mut ctl) = MockChild::new(123);
+        assert_eq!(child.pid(), 123);
+        ctl.exit_tx.take().unwrap().send(Some(0)).unwrap();
+        assert_eq!(child.wait().await.unwrap(), Some(0));
+    }
+
+    #[tokio::test]
+    async fn mock_child_terminate() {
+        let (mut child, mut ctl) = MockChild::new(1);
+        child.terminate().unwrap();
+        ctl.terminate_rx.try_recv().unwrap();
+    }
+}
diff --git a/crates/xy-supervisor/src/lib.rs b/crates/xy-supervisor/src/lib.rs
index 1747681..e536cee 100644
--- a/crates/xy-supervisor/src/lib.rs
+++ b/crates/xy-supervisor/src/lib.rs
@@ -1 +1,5 @@
 //! Process-supervision primitives for the xy daemon.
+
+pub mod child;
+
+pub use child::{ChildHandle, MockChild, MockChildController};