When the younger kid is a little older, that's a good time for him to learn what I call "The Secret".
I picked up on it many moons ago when I used to go to the original Yankee Stadium. I watched the pitchers, particularly the Yankees' Big Three rotation---Reynolds, Raschi and Lopat---and I saw what they were doing and how they were doing it. Those three guys were all doing the same thing; they were driving off the lower half of the body, using the legs, the hips and the torso in one continuous (and, it seemed to me, seamless) motion and creating a flow of energy right up through the shoulder and arm to the fingertips, thus generating more power in their pitches---and taking a lot of pressure off said extremities in the process. I saw just what they were doing, and I made a note of it so I could start working on this on my own. As I practiced this essential---and believe me, it is essential---element of good mechanics I found that I was doing exactly what those three pitchers were doing. Because I was a natural sidearmer I got the hang of it pretty quickly.
A good place to start would be the "Hershiser" drill, which aims to get the hips fully involved. It requires no special equipment, just a fence or a wall. The whole point is to get the whole body into the action, so that one doesn't throw with just the arm! :baseballpitcher: