You cannot forbid little children from going to the toilet. Firstly it's just not right (they have smaller bladders than us) and secondly it will be you that has to clear up the mess when you find the one's that REALLY did need to go to the toilet. Instead you have to find ways to discourage toilet breaks, and also ask beforehand if everyone has gone to the toilet.this goes two ways, yes martial arts instructors can deny potty breaks, even i do. but i did have one child actually pee on the floor during my class one day, no fault of my own actually, believe it or not i asked him multiple times if he needed to go! anyway, you can tell when a kid truly needs to go to the bathroom and when they do not, once over the age of 7 they should be able to hold it so, dont let em. but there are some kids that you can see it in their eyes and posture...LET THEM GO!!!haha trust me you'll thank yourself later. like i said previously i discourage potty breaks by adding the pushups on once they return. also each time someone asks me i ask them in a stern loud voice..."now why didnt we go before class???" and when i get a blank scared stare thats when i go..."go quickly, bow in and bow out or your dead. 20 pushups on the way back in!" also heres another hint, if the same child asks, every other class to go to the bathroom around the same time every class, they are just going for the fun of it, start cutting back.