Practices should not me more than an hour each, specially for young boys. Plus each day should vary, 1 day could be fiscal and the other 2 days juts practice goals or tactics. No need all practices bee really exhausting for the kids
It depends on your child and his endurance. I think 3 times a week is good, if you just want that your son be active. If you want that your son one day would become a professional, he must go like five times a week.