It's not true. I couldn't be an athlete in any popular sport, because I'm too skinny. I also don't have any excessive visual-spatial ability to master some low-paying, unpopular sport where size doesn't matter. As far as stuff like science and engineering, some people aren't smart enough for that. You should lead your children into what they're capable of doing. If they're interested in something but not very capable, then you need to let them know in a gentle manner that they might be able to contribute to it or be around it, but they can't be it. If you're a mediocre musician, you're not going to be Stevie Ray Vaughan, but you might be Tommy Shannon on the bass. You might play drums, that's even easier. You could also be a guitar tech or a roadie.