(OP here). The problem is that sometimes my barely five year old pees and then 30-40 minutes later has to pee again, especially if he drank a lot of water, which is feasible in the Florida heat. I could be in an 40-60 minute line and he could have to go again.
If it's inconvenient, I would ask if he can wait, but sometimes he can't. He's not twelve, he's five. I certainly would not insist he hold it because that's an unhealthy habit and I don't want him to risk an accident, which is embarrassing for him. It's not his fault if he already went before we got in line.
I completely appreciate what you all are saying about line jumpers (hadn't considered that) and some of the lines being narrow, etc. I can see it being less of an issue at some lines (like Monsters Inc off the top of my head), and almost impossible in others.
So, we'll do our best. It would obviously suck to wait in line for 40-60 minutes and then have to start over, but maybe we'd be close enough to the front at that point that we could ask a CM.
Or he'll just pee in a dark corner (kidding).