Wow, all the "stay away" replies. No wonder our country is turning into a wuss state. Geezus, let the kid ride, give him space. How the heck is he gonna learn??? It's his bike, his parents responsibility, if something happens, it's on them, not you.
Unless folks aren't confident of their own riding abilities, I say go with them, giv'em space and enjoy....
Just as long as members of the group know this, and don't outride him, he should hang just fine.
But that's just me, so..do what ya gotta do..