Meh.
Seems like just another kid. It's easy to just ignore him. I don't see the big problem here. It's Blockland. You expect all the people playing to be above the age of thirteen?
You're missing the point.
First off, it isn't "playing the game" that anyone is worried about. Blockland could be tons of fun for a young kid and I don't see any issues with it. I would say that multiplayer should be played at a parent's discretion, but the swear filter does pick up enough words that I don't think it would be a problem.
The point of this topic though is the forum usage of a 7 year old kid. A lot of inappropriate content can get through by way of forum Self Deletes or stretching rules. If I were in charge of that kid's welfare, I don't think I would allow him to use the forums. 12 and 13 year olds are frequently still too far immature for the forums.