New to karting. Motor question


Hi guys so happy I found this form. I bought my son a flat kart. It came with a predator motor. But they don’t have a class for his age. With that motor. He is 11 now but turning 12 in May. So I was going to run him in the Jr purple light and maybe the Jr purple heavy if he is ready for that. My question is what motors do you run in that class. I see flatheads and clones. I’m lost when it comes to what motor to run in each class. Thanks for all your help!