Kids on facebook is it ok?

my older son is on facebook he's 12 after seeing him playing the games on there and the arguments i had to through i let my 6 year old go on there too now you may think bad of me but my pc is wired up to the tv i can see everything he does i know who he talks to what he does everything he only actually goes on there to play monster galaxy i have noticed alot of the games are aimed at the younger ones well the headmistress at my sons school has had the police in and have deleted my son and his friends account now for a school which is really bad on bullying and does not have a very good reputation i think to be honest she had no right in doing this and should be concentrating more on what goes on in the school not out of it im really quite mad she had the cheek to do this she use to be a teacher and since being made head has gone really power mad