That's an awfully depressing way to look at it. Every kid watched professional sports growing up and said, "Man, I want to make the game winning touchdown." Or, "I want to sink that 10 footer on the 18th hole at Augusta to win the green jacket."
I don't know if my future kids can be professional athletes or not, but I know one thing for damn sure, I'm going to encourage them to try. Telling your kids that they can't be something that they want to be is sad. That's just telling them to admit defeat, roll over, and be a nobody for the rest of their life.
You may choose to do that with your children, but I sure as hell won't be taking the same approach.