Hi,
As Akien said, please post more details about the issue. A more accurate description of the problem, some screenshots/videos, your PC info (Processor, RAM, OS, and Graphics Card Especially), and play around with graphics settings some to see if enabling/disabling anything solves the problem.

There was a thread opened a few months ago that said Green Valley got very slow, choppy, and nearly unplayable as you went up the road from the starting line in 0.8.1. I had this same problem on my computer and solved it by reducing the game resolution. Not sure if this is the issue you're experiencing, but it's worth a try.

Hope this is somewhat helpful and I hope your son is having fun with SuperTuxKart. I have younger siblings that are his age too and they love playing it on my computer.
