As far as youth sports go, it's much better for kids to play multiple sports. The specialization really shouldn't come until high school, if not college, and that's for multiple reasons. One, doing the same activity all year long does lead to overuse injuries and a lot of muscular imbalances. And if you're doing that, you oftentimes don't get adequate rest because you're doing the same sport the whole entire year. Whereas if you're changing sports, it, one, gives ... For example, if you're a baseball player, it oftentimes can give your arm, your shoulder, your elbow time to recover while you're doing basketball or football or whatever sport you choose to play, while also you get a completely different set of muscles and tendons and bone stresses, if you want to call it that, where over time that's good for preventing the muscle imbalances and problems with overuse injuries.
