Hi S.. I'm coming to you from the viewpoint of a mom with two boys who played soccer, baseball, and swam for years while they were young. (Swimming ended up being the sport that stuck.)
Neither of my kids have ADHD, but my younger one was very active. So I'll talk about him. He used to look at the bugs on the field, the clouds in the sky and wave at people in the stands. The coaches had several little boys like this. They were understanding about the attention span. They moved the practices quickly and gave POSITIVE reinforcement for what the kids did WELL.
What you don't want to do is make this a-season-to-remember being yelled at all the time because he wasn't on task. Calling to him with reminders is one thing. Bawling him out for missing a ball is another. Teach them baseball terms and what they mean, like "Now you're ready!", "Heads-up!", "Call it!", "Full count" and hand signals for the strikes. That way, you can say the SAME WORDS for the kids as a group, and to the children personally ("Heads-up, Johnny!" when the ball is coming his way) and he won't feel that he is being singled out and yelled at.
DO NOT allow parents to badmouth a child. Stop a game if you have to and go to the stands and tell a parent who is being inappropriate to stop. It's best to send an email to the parents in advance and tell them that bad behavior from the stands won't be tolerated (an ounce of prevention is worth a pound of cure type thing). And you have to stick to your guns and mean it if someone does it anyway.
You most likely do not have kids in your group who are destined for the pros. You may have kids who will one day make the travel team. You can teach baseball and be kind at the same time.
I'll end this telling you what I dealt with in my younger child's first soccer season. (I think he was 6.) My son was one of the best players on the team. They were playing one of the games with a team whose coach decided that the way to coach was to make his players little hoodlums. His kids were aggressive and fouling every which way but loose. He egged it on yelling at the kids to "go for it". Long story short, the game ended abruptly when a kid slammed his elbow into my son's face, giving him a horrendous nosebleed. Mothers on our team were crying, they were so upset, and not just because of my son's nosebleed, but because the game was so awful and the coach agressively encouraged his kids' behavior. After going through this, I have always appreciated children's coaches who weren't trying to recreate their own glory days using children to do it. Thank YOU in advance for caring about your kids.