Should young athletes play more then one sport?
In a word...yes.
If i told you that because your daughter liked math and was good at it, you should remove every other academic topic from her daily, month and annual calendar and only allow her to learn math, would you believe that this was a good idea?
Would you argue that the only way to eventually become an authority in a given area of study was to have a well-rounded brain, rich in exposure to other subjects like English, History and Biology?
Well....you'd be right!
Now, all you need to do is apply that same logic to sports.
To become the best baseball player possible, you must first become the best athlete you can be. Early immersion in any specific sport is the single greatest cause I have ever seen to young athletes not living up to their potential. The basis for this reasoning (if you need more then the first paragraph above) is due to the plastic nature of the nervous system that exists while we are young. To be plastic means to be adaptable - kids are inherently more adaptable than adults, and the reason they are better suited to lean new languages or athletic skills over us. The more exposure a young person has to a diverse array of sporting opportunities the more able they will be to learn, master and perfect the advanced skills involved in any sport you can name.
The very best sports specialists in the world are also the best athletes. Its just that simple.
Need more proof? Tom Brady, the New England Patriots QB, excelled in both high school football AND baseball