diff --git a/CHANGELOG.md b/CHANGELOG.md
index e0d596b9..7cf50f6e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,6 +12,7 @@ and this project adheres to
 
 - ♿(frontend) improve accessibility:
   - #1354
+  - ✨fix tree keyboard toggle when children not yet loaded #1388
 
 ### Fixed
 
diff --git a/src/frontend/apps/impress/src/features/docs/doc-tree/components/DocSubPageItem.tsx b/src/frontend/apps/impress/src/features/docs/doc-tree/components/DocSubPageItem.tsx
index 0b0ee038..46e86ed4 100644
--- a/src/frontend/apps/impress/src/features/docs/doc-tree/components/DocSubPageItem.tsx
+++ b/src/frontend/apps/impress/src/features/docs/doc-tree/components/DocSubPageItem.tsx
@@ -20,6 +20,7 @@ import { useLeftPanelStore } from '@/features/left-panel';
 import { useResponsiveStore } from '@/stores';
 
 import { useKeyboardActivation } from '../hooks/useKeyboardActivation';
+import { useLoadChildrenOnOpen } from '../hooks/useLoadChildrenOnOpen';
 
 import SubPageIcon from './../assets/sub-page-logo.svg';
 import { DocTreeItemActions } from './DocTreeItemActions';
@@ -96,6 +97,14 @@ export const DocSubPageItem = (props: TreeViewNodeProps<Doc>) => {
     '.c__tree-view',
   );
 
+  useLoadChildrenOnOpen(
+    node.data.value.id,
+    node.isOpen,
+    treeContext?.treeData.handleLoadChildren,
+    treeContext?.treeData.setChildren,
+    (doc.children?.length ?? 0) > 0 || doc.childrenCount === 0,
+  );
+
   const docTitle = doc.title || untitledDocument;
   const hasChildren = (doc.children?.length || 0) > 0;
   const isExpanded = node.isOpen;
diff --git a/src/frontend/apps/impress/src/features/docs/doc-tree/hooks/useLoadChildrenOnOpen.ts b/src/frontend/apps/impress/src/features/docs/doc-tree/hooks/useLoadChildrenOnOpen.ts
new file mode 100644
index 00000000..445e74e9
--- /dev/null
+++ b/src/frontend/apps/impress/src/features/docs/doc-tree/hooks/useLoadChildrenOnOpen.ts
@@ -0,0 +1,51 @@
+import { useEffect, useRef } from 'react';
+
+/**
+ * Lazily loads children for a tree node the first time it is expanded.
+ */
+export const useLoadChildrenOnOpen = <T>(
+  nodeId: string,
+  isOpen: boolean,
+  handleLoadChildren?: (id: string, signal: AbortSignal) => Promise<T[]>,
+  setChildren?: (id: string, children: T[]) => void,
+  isAlreadyLoaded: boolean = false,
+) => {
+  const hasLoadedRef = useRef(false);
+
+  // Reset only if node changes AND it's not already loaded externally
+  useEffect(() => {
+    hasLoadedRef.current = isAlreadyLoaded;
+  }, [nodeId, isAlreadyLoaded]);
+
+  useEffect(() => {
+    if (!isOpen) {
+      return;
+    }
+    if (isAlreadyLoaded || hasLoadedRef.current) {
+      return;
+    }
+    if (!handleLoadChildren || !setChildren) {
+      return;
+    }
+
+    const abortCtrl = new AbortController();
+    hasLoadedRef.current = true; // prevent multiple fetches
+
+    void handleLoadChildren(nodeId, abortCtrl.signal)
+      .then((children) => {
+        if (!abortCtrl.signal.aborted) {
+          setChildren(nodeId, children);
+        }
+      })
+      .catch(() => {
+        // allow retry on next open
+        if (!abortCtrl.signal.aborted) {
+          hasLoadedRef.current = false;
+        }
+      });
+
+    return () => {
+      abortCtrl.abort();
+    };
+  }, [isOpen, nodeId, handleLoadChildren, setChildren, isAlreadyLoaded]);
+};