My son figured out how to lock himself in the bathroom. Now he does it all the time. Whenever we have a babysitter over he locks himself in there. We've had to come home early several times because he just won't behave. We started warning the babysitters that he was doing it and showed them where the master key was but then he took the key, locked himself in the bathroom and started crying, saying he was bleeding. The babysitter broke down the door and he was laughing. We took the lock off his bathroom but then he started hiding in ours. How can I control this situation without having to give up the lock in my bathroom?