During the weekend, after one trip to a public restroom with my youngest (5yo) son, I reminded him what that slot in the front of his underwear is used for.
Typically, when he pees, he simply pulls down his pants and underwear -- exposing his rear to the rest of any restroom users. So, being a good dad, I stand behind him, facing out, to give him some privacy and keep his rear as unexposed as possible.
This morning while I was shaving, my son came into the bathroom to do his own business at the toilet. He proudly said that Tuesday while at school, he went to the potty, pulled down his pants as usual -- but kept his underwear up and stood there doing his business using that slot (door?) in his underwear as it's supposed to be used.
I am such a proud dad!