Study: Overuse, Not Curveballs, Leads to Injuries").
The American Sports Medicine Institute, which was founded by orthopedic surgeon James Andrews, recently conducted a similar study and arrived at the same conclusion: while curveballs can be harmful if they prevent young pitchers from mastering the mechanics of throwing a baseball, they don't directly cause injuries. In fact, a separate study by the institute found that the amount of force required to throw a curveball is equal to or less than the force required for a fastball, which means that throwing a curveball may be less harmful to young arms than fastballs.
The moral of the story? If your son or daughter is a pitcher, make sure they take time off from pitching. Let them play other sports: basketball, soccer, cross-country, golf, volleyball. They'll help increase your child's coordination and dexterity, which will benefit their baseball playing abilities, while at the same time giving their arms a much needed rest.