When Mick and I play, he'll open his mouth and sometimes "bite" me, but he'll never close his mouth. Then if we're just standing around and I'll try to stick my hand in his mouth he won't even open it.

Cincy'sMom kinda said what I would have. They probably see you as an equal because your the one playing with them. (Unless your Mom regularly plays with them too, I don't know)