I can't imagine telling my kids or grandkids (which I don't yet have) that they can't use the bathroom in the RV.
There are some exceptions to this as I have 4 boys and, well they are boys after all. I have/had only two bathroom rules. Everybody has to sit to pee, no exceptions. Boys have a tendency to miss from time to time so I started from day one with that rule.
The second rule is when remote camping or boondocking. If it's daytime and you're a boy you have to find an outside bush to go pee. The girls get to use the bathroom every time.