Your son will have lots of fun, just be careful! My frist time out I could not cou nt how many times I flipped and I sn apped my flag twice. Of course I do it at the dunes though.
Those Yamahas are nice bikes and they really scream with a nice pipe. Take a look at the Sparks pipe. Curtis Sparks is a real nice guy as he is a local and will help you if you have any questions.