I have never heard of games starting by themselves ... wonder if that's a setting thing ... though didn't even know you could do that.
Maybe he entered tournaments or team matches? That's all I can think of...
Yes, he appears to be participating in a number of tournaments. That's probably it.
Eight year's old you say? I couldn't make my son to play, if I beat him with stick.
When creating an open challenge in online games, there is a check box at the bottom of the challenge set up which shows
"Automatically start my game if similar seek is found."
If this is checked, the games will start automatically without him having the option to accept or decline.
Do not accept nor register for those matches, you can cancel them before making any move, if you did, cause after the forth move cancelling will effect your rating negative.