High school teams tend to be as good as the rec leagues that feed them; and, some of the most successful high school coaches I've known over the years have put a great deal of effort into assisting and supporting the rec leagues that send players up to them. Most have done so as a long-term effort; helping them make incremental improvements over time that steadily improved the quality of player they produced.
The coaches do so in a variety of ways; but, it begins in establishing a close relationship with the rec league officials who are directly responsible for baseball at each local league. If you're not currently involved with them, I'd recommend that you sit down with them and make an assessment of what each needs. Chances are, there will be elements of their program that you'll be able to help them improve.
The better they are, the better your team becomes. Dedicated effort on this front will pay you long-term dividends. I've seen it in a number of cases.
I think this is very true. Another thing the OP should consider is getting into travel ball, if he's not already. He could help the best of those 12U and under rec players develop in the fall and summer, and also get his HS team culture started early. Around here, HS coaches with successful travel teams have players transfer into their schools, not out of them.