Fortunately there's a big gap between "College kids" and "Kids", and by the time you're in college it's not just about having fun anymore. Sports in college, whether we like it or not, are a large source of upward mobility for a lot of people, sometimes whole families and communities. College sports can determine access to college through the system of scholarships, and of course they can lead directly to pro careers.
Generally speaking when people talk about "kids sports" they specifically mean pre-collegiate, not in the least because colloquialism aside, college students are adults.
> by the time you're in college it's not just about having fun anymore
As someone who played sports in college, for >99% of people it really was just about having fun: you're hanging out with your friends, getting some exercise, and doing something enjoyable. I exercised side-by-side with people who went on to represent my country on the international stage and their dedication was definitely the exception.
No silly scholarships involved here, though: I live in the EU, so education is reasonably affordable to everyone without it, and the colleges don't feel the need to pretend to be professional sports teams.
Generally speaking when people talk about "kids sports" they specifically mean pre-collegiate, not in the least because colloquialism aside, college students are adults.