That is a conundrum in our sport and has been for a long time. For a casual riding family that will buy a kid a "fun" bike that they can ride anytime, there isn't much in the way of classes to race. A lot of my friends ride in the woods and buy their kids the same bike or similar that you have and unfortunately unless a club or promoter creates a class for them, there isn't much available. A lot of them have moved on to the family enduros that group kids by age with no real bike restrictions and they have been really happy with that.