Cannot remember password on ipad 4 and unable to unlock it

My kids all have ipads, and my son got his taken away because of his grades being bad. I put it away for a month and the battery was dead when I finally gave it back to him. Once it was charged, he tried to log into it and could not remember his password. I followed the directions on apple's website and did a restore and after that it is stuck on the activation screen and it is still asking for his user name and password. He is only 11 years old, and I was not aware he had set up the account with a password. How do I get it to unlock not knowing any of what he used since he cannot remember any of it either? It is useless without being able to unlock it so he can play with it. Help!