T.S.
You should get Kidoz. It's a whole browser for kids to use. My son is 5 and has been using it for two years. We love it. Instead of dealing with blocking stuff... you put in the sites he CAN go to. Everything is icon based, it's awesome... plus he gets his own little webmail account (but he can only send or receive from friends or family YOU set up as contact... you can even make all the messages filter through your account.)
A quick google search for kidoz will be well worth your time.