My son playes baseball, and he gets bad leg cramps (charlie horses). is it ok for him to have potassium pills or should i give him some else?

Probably Not: A healthy 9 year old who eats a regular diet should not have issues with low potassium unless there is some underlying problem. Low magnesium can also cause leg cramps. Instead of giving potassium pills i would suggest just a regular children's multivitamin. If the problem does not resolve with this i would have his pediatrician check a complete metabolic panel to look for any abnormalities.