OP, you're all over the place. You went from "time for pants buddy, dinner's almost ready" (seems like he wasn't causing any major problems) to saying he's urinated in the flower pot before and he's having problems at school. It went from a backyard dinner where the kid wearing a sweatshirt wasn't questioned to a formal dinner with everyone in "church attire."
If you really just wanted to see if others think that 5 is old enough to expect pants, you could have just asked that. The fact that you included ALL that other info comes across as if you want validation, or even praise, for correcting him. Now, that's not necessarily why you posted, but that is how it looks.