Yes, the do think and behave like children

This is why it is so difficult to have a rational conversation with a narcissist.
My big mistake, was I kept talking to him as if he was a normal person and
expecting him to "just get it."  He is never going to GET IT.  His brain is stunted
somewhere in late teen years.  He is in an adult body and can act like an adult most
of the time except when it comes to emotional reactions.

From: Stop Caretaking the Borderline or Narcissist by Margalis Fjeldstad