Interesting discussion. I have a 14yr old 2020 who is around 6'2" and 195lbs. He's a late bloomer in that he didn't really start to take sports seriously until last year when he was on the middle school football, basketball and baseball team. He knew heading into this year that playing time on JV football would be tough to come buy and making the other teams where there are cuts would be difficult as a freshman.
He spent most of the summer going to "speed camp" 4 afternoons a week with a few other kids at a gym we have been going to for years for our 2016. Lots of sprints, footwork drills, working on form, explosive movements instead of steady cardio. He also lifted on his own at the gym (he has worked out with the trainers in the past to put together a workout and work on form). I think that really helped him with coordination and body awareness - things he had been lacking at that size at an early age. That combined with the football workouts in two a days and then 6 days a week after have left him a very large person in excellent shape. I asked him to try to touch the rim the other day and he took three steps and got about his entire hand over it.
So the other thing I would recommend - have them play fall and winter sports instead of just continuing baseball and off season workouts until they get further into high school and have to make a decision on one sport (if they do, I know some kids don't need too). Playing football, soccer, basketball will get them in much better shape and work lots of different muscles than playing baseball. Even just practicing/working out (if they end up on the bench during games) will help them become better overall athletes.