Back in the day, people used to say silly things like "it will stunt your growth, it will slow you down, it will make you muscle bound..." if a young athlete wanted to train with weights. While this may be true of traditional
weight training (bodybuilding) it is otherwise FALSE.
http://www.nsca.com/education/articles/why-youth-strength-and-conditioning-matters/
We train young people the same way we train older people, individually. We assess their abilities, we design a program, the program has goals, the goals display effectiveness, we assess again, and again, and again. Yes, young people are not fully developed yet. This provides an opportunity for us to teach positioning, timing, work ethics, and coachability. Their skeletons are not fused yet. The addition of a load upon this developing system builds thicker, stronger, more resilient bones and connective soft tissues not to mention muscles Also, the Motor Unit (MU) recruitment patterns developed during an extended, fundamental, starting cycle of training.
These girls have abilities needed in other sports. They are fast, strong, agile, can jump very well, have great reaction time, and think on a finer scale than other athletes.
Young people need to train maybe even more than old people.
Get stronger!