It is at least possible that the CM thought they were paying a compliment to the kid. As in "Aren't you a little big to be pushed around - you're almost as big as me and you get a ride! Boy, I wish I could get a ride too - can we trade places?"
If you kind of think of it in that context, and with the right tone of voice, and given that CM's are taught to be engaging to the guests- I can see where MAYBE the intent was not to be rude. Also, I know I might make the mistake of "well, if there was a medical issue, he'd be in a wheelchair - but I don't see a wheelchair, so if anything is safe, this next comment must be..."
Now, before you point the flamethrower at me - it was still inconsierate. But I wouldn't have blown up in the CM's face or reported them. Ruining their day or getting them fired doesn't help any of us really. In fact, it may actually cause the 'flight' of CMs who mean well but suffer from youth - in favor of CMs who punch the clock, don't smile, don't speak and therefore never risk getting reported.
I think the OP responded appropriately. The CM, assuming they are a good person, probably learned a quick lesson and won't repeat the mistake - and that DOES help all of us. That lesson was served appropriately and didn't risk 'souring' the CM. This was a sin of omission, not comission - it wasn't deliberate or malicious.
I say let the CM live to see another day
