My son was a late bloomer, so we didn't know that he could play in high school until he was in high school. His LL team won the sectionals. . . but he did not play much since the dad who coached considered him a wild card on the mound. He tried to play third in middle and high school but a kid a grade above him owned that spot. My son grew about 6" in his sophomore year. At that point, he was so much better as a kicker in football---but he thought it was kind of a lonely position. So, he tried pitching again . . . and this time he just seemed to figure it out (of course with a lot of hard work and a great coach) but still, pretty unexpectedly considering he started as a second-string third baseman at 15. He had an area code tryout as a RHP at 17. So, all that happened over just 24 months, which is just a blink of an eye to us adults.
Kids are so changeable. I think you can know if your child is athletic or not and if your child is disciplined or free-wheeling, but @PTWood is right -- you can never really know what will happen.
I like what JucoDad wrote: "Partly due to ignorance, partly due to the way I’m built I never looked too far out or “knew” too much. The whole journey is so fragile/special, and my goal was not to be disappointed when it ended." What a great attitude! I hope I can adopt it too!