I for one, don't believe in parents forcing their kids to start being serious at a young age.. in the sense of forcing them to training or forcing them to do this or that. I prefer the word encourage. Encourage them to take up an outdoor activity and get out more.
I have passed throught the junior ranks in aussie tennis and in my time I have seen many such 'sports parents'. The full-on fanatical kind.
Most of these 'sports parents' kids are pretty damn good at the earlier ages, but when you hit the 16 - 18 age groups, you can see that some of them tend to just fall behind - burn out etc.
The point is, the motivation must come from the kid themselves and a pressurising parent may kill that motivation.