I guess it depends on the TSA agent, but while you don't have to have ID for a child, some agents will ask the child questions. My DS is 8, we've flown on 3 trips in the last year, and each time he's been asked (and we, too fly out of Boston) his first and last name and to identify the people (DH and I) that he's with. It threw us all for a loop the first time it happened (and being a doting mom, I tried to answer for him but the agent semi-nicely said she wasn't talking to me, she was talking to him!). So along with all the other great advice you've already gotten, I would have the kid prepared to answer calmly and clearly, "My name is Joe Guy," and if the agent wants to know more, be able to say, "these are my best friend's parents, and I have a written note from my parents giving them the approval to take me on this trip to Disneyworld" or whatever.