This is a position statement from the American Sports Medicine Institute:

http://www.leaguelineup.com/northedison/files/ASMI%20Position%20Statement%20Final%20Pitching.pdf

"Throwing curveballs has been suggested as a risk factor, but the existing research does not support this concern. However, a youth
pitcher may not have enough physical development, neuromuscular control, and proper coaching instruction to throw a curveball with
good mechanics. Throwing curveballs too early may be counter-productive, leading to arm fatigue as well as limiting the youth’s ability
to master fastball mechanics."

Other highlights:

- Rest pitchers that appear tired (duh)
- No overhead throwing of any kind for at least 2-3 months per year (4 months is preferred) - this is currently the biggest problem IMO
- Follow limits for pitch counts and days rest
- Avoid pitching on multiple teams with overlapping seasons (another huge problem)
- Learn good throwing mechanics in order - 1) basic throwing, 2)fastball pitching, 3) change-up pitching (notice no curveball)
- Avoid using radar guns.
- A pitcher should not also be a catcher for his team
- Let kids have fun and encourage them to play other sports