They, as a minor, do not help constitute the quorum nor lead the congregation, although they do count for kaddish.
What about someone mentally defective, like some autistic or retarded. Matilda, in particular, tells us, "I had come to know this Pip as if he were real. http://Nlifelab.org/bbs/board.php?bo_table=free&wr_id=3269958