RE: Kids starting on a CARVE99  with kids rig
This is a tough question as how to answer it depends entirely on how you decide to teach your boys.
If you plan to ride on the board with them at first, (the fastest and safest way for them to learn) it would have to be the 180 liter Nova and even then I'm not sure there's enough float.
If the boys are going to sail it by themselves, right from the start, then the Nova 165 would be better for them individually.
Please take a look at the other thread here and what I've suggested about "teaching your own".
Hope to see you in Plattsburgh, which would solve this problem.