I don't think the subchild returned is a node3D object that you can scale and call most node3D commands on. It's more like a texture that can be modified in terms of visibility and alpha. If you want to scale the head the best would be to to this in 3ds Max and re-export the meshes. That way you could also adjust the neck of the body mesh. Another option would be to create a
Peoplemaker head that you could scale in Vizard.