In Foof Engine, every physical object in the scene can have children. These children can be bound to specific bones in the parent, so this can enable things like mounting weapons to hands and what not. The bone-bound children get their positions updated when the parent is animated.
Physical objects include all meshes, billboards, lights, cameras, etc.
LInk to video here: http://www.youtube.com/watch?v=CplWtqgdig0