How To Set Up Skeletal Animation In Your Scene
When you upload a model with a skeletal animation in it, everything will be set up correctly for you. Your scene graph will have the structure below.
If ever you want to manually set up scenes with skeletal animation, you must follow this structure.

A more precise view of the entity hierarchy:

Root: Entity with animation controller. A compatible animation graph and animation set are assigned to the animation controller. The skeleton the animation set’s animations depend on should be the same skeleton that is referenced by the skinned mesh entity.
Skinned Mesh: Entity with skeleton reference and mesh reference. The mesh should be a skinned mesh and the skeleton should be compatible with it (e.g. they were converted from the same source file).
Skeleton Root Bone: This entity and its children are a hierarchy that mirrors the skeleton. It is created automatically for you when you upload a file with a skeletal animation. It’s optional.