Skylark, if the fastball is the cause of most arm injuries I guess most kids shouldn't throw fastballs, right? Perhaps frisbees? Baseball is a game built around the fastball. Without it, without a good fastball, it is impossible for any kid to pitch at the "next level", whether that level is travel ball, h.s., college or beyond.
Throwing a fastball is by definition "fast". It is a calculated risk to throw a baseball fast. But not doing so would seal the fate of most any pitcher. Hang up the cleats, go bowling or join a choir, because your baseball days are over. Read all the studies that tell you it is so stressful and make your choice. Quit the game or take the chance. Without it you quit the game. Period.
Not so when determining which secondary pitches to throw. The changeup at the lower levels, while effective, is usually thrown improperly and detracts from the ultimate goal (to develop and learn how to command a good fastball). Kids slow their delivery, open up, and engage in trickery all of which might work but each time one is thrown it is subtracting from the gain that could be had learning to command a hard fastball.
Get to college, and you will quickly learn that kiddie change is merely a BP fastball that goes yard. Don't kid yourself, your changeup in h.s. is a meatball. Have fun with it, throw it, get people out with it, but it's subtracting from your development. Try to sign with a D1 college with an average fastball and a B.P. changeup. Not going to happen!.
So you need a solid FASTball and a secondary (breaking) pitch. Again, the secondary pitch is NOT a B.P. fastball. That leaves few other options, so choose: a college slider, which will tell your arm "I'm toast" in a year or two or a curveball, which if thrown properly, is harmless.
Skylark, I've seen enough of the college sliders to know they're worthless AND dangerous.
I'm NOT saying changeups are bad. Just consistently saying the changeup in h.s. and in college and beyond are two different pitches. Two different pitches!