He doesn't really interact with the group. Some days he will just sit with a toy/book/anything and not move at all, despite encouragement from myself and the other kids. He does not speak here, no communication at all. I will as yes/no answers, he sometimes nods, but most of the time his nod is "wrong."

There have been no changes in routine or children. I am an lnr, so only have 3 kids total. During circle time, he doesn't participate. No laughing, movement, engagement.

His mother does assure me he's active and chatty at home.

Ideas on how to help him break out of his shell here? Other than possible underlying issues, that mom says he is fine, could there be attachment issues, situational "hermit-ness," or situational uber introvert?