But is it right to teach children to stop playing sports so they can play sports video games?
You seem to assume a swap between a virtual activity and a real one. Exchanging one for the other. Simulating a thing in a video game, so you can avoid the thing in reality.
If you believe this is possible, it should apply to all other activites in video games as well. Including killing people. And that discussion was done ad nauseam. It's just not true. Playing a video game is not the same as doing a thing in real life.
You might construct trivial examples, where it could be so, like playing online poker or chess.
But your concern is the same that's with any non physical activity. Like watching television. Or even reading. You should not focus on that one tiny aspect where coincidentally some kids would play virtual tennis, instead of actual tennis. There is not really a difference from them not playing tennis, because they play virtual tennis, play minecraft, watch netflix or read vampire novels. They're not jumping around in either case.
As you say, playing sports games is always right because it's fun.
I did not say that. I explained the reason why someone would play. And that reason usually boils down to fun. There are other reasons too, but all this is not touching the morality of "wasting time with games, instead of some socially approved recreational activity".