Years ago, young athletes would play a variety of sports, go on vacations with the family, and have months for an "off season." Nowadays, it is not unusual to see a 10-year-old playing 100+ baseball games in the summer, cramming in $60 personal training sessions 2 times a week, hitting and pitching lessons 3 times a week, and then squeeze in some strength and conditioning training between practices.
Baseball pitchers who play for multiple teams with overlapping seasons are at increased risk of injury from exceeding
mandatory or recommended pitch limits. 
While playing on more than one team at a time may give an athlete more opportunities to develop his skills, and while the amount of pitching may be limited by league rule or the judgment of the coaches, it also increases the risk that he/she may end up exceeding mandatory (in the case of Little League) or recommended (in the case of USA Baseball) pitch limits (or the 100 inning per season limit recommended by the American Sports Medicine Institute in its 2010 study).
Because of a lack of communication and coordination between coaches, it may be up to you, as his parent, to keep track your child's pitch counts and days off and to insist that the coaches not exceed those overall limits. If you don't, the coaches are going to end up blaming each other if your child suffers an arm injury.
Posted March 28, 2011
