Regardless how serious your youngster is, or will be, the training cycle that I've pictured below is a good plan to start with.
As you all progress just keep in mind that any lack of interest or distraction with any one discipline means a weak link in the total plan - that is, to give your son the oportunity to enjoy and benefit with his overall experience.
If he's got baseball in his future, any baseball, every level will expect greater and greater demands on his ability to focus and produce. If he's just in it for the park-n-rec experience, he'll have a good time and be healthy at the same time. If he's got a "program guy" kind of game, he'll out shine the majority of prospects competing for a roster slot.
Why do I say out shine? Because so many players start out with 100% effort, but the body and mind start to lose %'s as time goes on when they haven't address this basic training cycle as shown below.
Each discipline that I've shown below is a lenghthy topic all by itself and goes well beyond this posting - BUT, you're off to a good start.
Find yourself a PROFESSIONAL pitching coach, tailored to your son's age and personality. It's money well spent and you'll both have a great father and son experience.