My oldest started throwing a curve ball at 9 or 10 and had great success with it. He won many games and was always an Allstar selection. He continued through Minors, Majors and into high school. He had such an outstanding curveball that he made the Varsity team as an 8th grader. His success contined all through high school and everyone thought from early on that he would play college ball...
The problem was that his curveball was 74-75MPH and his fastball was 75-79 and his change was 72-74...not very good. And while his curveball was excellent and he piled up the wins with it, he just never developed anything else. So dispite his success, he was not recruited and he had to learn after high school how to throw a fastball.
Ultimately, he took some time off after high school and developed a fastball and ended up walking on and getting a scholarship at a JC, but Holy Cow, what a learning experience!!
My 11 year old knows how to throw a curve ball and I let him throw it some, but 90% of his pitches are FB and the majority of the rest are change-ups. The curveball stays on the shelf for the most part.
My 2 cents.
R.