It is time to follow through.
Execute the rules that you stated in that first week. For example, if they ask you to go to the bathroom at a time that is not okay, then you must say no and remind them that they must go between classes or whatever it is that you have told them. Then, at a time that is not embarrassing in any way to the child who "forgot" the rules, you should remind the class what the rule is. If you allow the child who "forgot" the rule about the bathroom to actually go to the bathroom, you will have that problem all year long. … With many, many children. That problem will take over your room like a bad weed in a beautiful garden.
Of course… There are emergencies that we must be able to recognize. As a young teacher, this was not always easy for me. We must use our careful, sound, adult judgment.