My kids started the travel ball at 9. I helped coach and took this issue very seriously. We read everything we could get our hands on to understand the best thinking available and we lost games because we wouldn't bring a kid back after he reached our predetermined limits.
Saw a 9 year old throw 129 pitches against us. Next year had elbow surgery and never pitched again. We played that team off and on for another 4 years. It was sad. His grandfather approached our Head coach once and had a conversation with him and was stunned to hear we remembered his grandson and shared our approach. The old man cried and said that he wished his grandson had played for people trying to act that responsibly.
I don't know if we were lucky or did the right thing but every player we ever had got to HS with their arms intact and to my knowledge has never had a serious arm injury. I do believe if you are going to get involved with coaching a travel team...and let's face it about 90+ are run by well meaning fathers up to HS, I do believe that getting up to speed in this area is a must and then making a plan and sticking to it.
I always said that no one will remember who won the 10U Easter one day Tourney in any town USA but they might remember a player in the game if he stays healthy to play ball long enough to find how good they might be.