.

Engine/src/Scene/Hierarchy.cs

@@ -50,6 +50,9 @@ public class Hierarchy<T>
 
     _hierarchyActions.Enqueue(() =>
     {
+      if (!Contains(parObj))
+        return;
+
       var parent = GetParent(parObj);
       _childrenLookup[parent].Remove(parObj);
 
@@ -97,9 +100,24 @@ public class Hierarchy<T>
       : throw new InvalidOperationException($"Child {parChild} is not in hierarchy");
   }
 
-  public IEnumerable<T> GetChildren(T? parObj = null)
+  public IEnumerable<T> GetChildren(T? parParent = null)
   {
-    return _childrenLookup.TryGetValue(parObj, out IList<T>? children) ? children : Enumerable.Empty<T>();
+    return _childrenLookup.TryGetValue(parParent, out var children) ? children : Enumerable.Empty<T>();
+  }
+
+  public IEnumerable<T> GetAllChildren(T? parParent = null)
+  {
+    var children = GetChildren(parParent);
+
+    foreach (var child in children)
+    {
+      foreach (var descendant in GetAllChildren(child))
+      {
+        yield return descendant;
+      }
+
+      yield return child;
+    }
   }
 
   public bool IsInHierarchy(T? parAncestor, T? parChild)
@@ -133,19 +151,4 @@ public class Hierarchy<T>
 
     return IsInHierarchy(parAncestor, parent);
   }
-
-  public IEnumerable<T> GetAllChildren(T? parObj = null)
-  {
-    IEnumerable<T>? children = GetChildren(parObj);
-
-    foreach (var child in children)
-    {
-      yield return child;
-
-      foreach (var descendant in GetAllChildren(child))
-      {
-        yield return descendant;
-      }
-    }
-  }
 }