Why does the RotationCube in HelloCube-Reparenting have Child components from the beginning

[00nico00]

When I was reproducing the HelloCube-Reparenting example, I directly right-clicked on the RotationCube to create a new child object, Cube. This parent-child relationship only exists within the UnityEditor and does not involve ECS Parent and Child components (originally, I thought this relationship would be automatically converted during baking). As a result, I encountered errors when reproducing it on my own (until I initialized attached as false). When I examined the scene of the official example, I noticed that the RotationCube comes with a Child Buffe. I would like to know how this was achieved.