How to merge an object onto a rigged character?

I’m trying to add eyes and teeth to a pre-rigged character. One thing I tried was making them children of the character prefab, and I also tried putting them all in an empty game object. When I run the program, the body moves but the added parts stay stationary. Is there a way I can get them to move together?

You should be able to add them as child objects to the specific bones of the character you want them to be attached to.