"I don't know"

I taught TJ to say "I don't know" with hand signs. Usually, when he is stumped for the answer, he just says...hrump.. kinda in his throat. He learned to say "me" a few months ago, to the question "who is it" preceded by knock knock on the bathroom door. He started by saying 'TJ' to "who is it?"but, once I told him to say "me", he never said "TJ" again. Pronouns are not the easiest thing for little ones. TJ says 'Thomas' [the tank engine] every day of his life now. While out with his dad, someone official ask Tom is name.......Tom said, "Thomas." TJ was surprised to find out that his Dad {Tom} had the same name as 'Thomas the tank Engine.' Every day is special, wonderful and amazing to TJ and to the Grandma, who shares a lot of each day with him.