I've coached my kids for a few years. I agree snacks are going to be way more important to them than anything else. Another big draw for them will be playing in the dirt when they're supposed to be paying attention. Do you have an assistant coach? You'll need one. Someone needs to manage the chaos in the dugout while you're coaching first or third.
Your reluctance to have them throw to each other is understandable. They should be playing with compression balls or "reduced injury factor" baseballs. They're the same size as a regular ball but more squishy. My son is 6, was probably the best player on his team (bragging, but it's not like he had much competition), but he is lousy at throwing and catching. We had to practice that, so when we go out in the yard to play catch, I make him wear a helmet with a faceguard. It allows him to focus on what I'm trying to teach him without fear of losing teeth. Plus this way, I can throw harder, watch him take one off the faceguard, and say "See? I told you to get your hand up!" without feeling like a horrible dad.
As for what to teach, don't get too ambitious. Teach them to get the guy out at first. It would take you all season to get across the concept of a force out at any other base. Also teach them to catch a ball with their fingers up. A ball below their knees- fingers down. Everything else- fingers up. This sounds dumb, but if they can get that straight, it greatly reduces the chances of catching a ball in the mouth. All the time I see kids trying to catch a ball above their shoulders with their palms to the sky. Bad idea.
Your practices shouldn't be more than an hour so you won't be able to get much done no matter what. They'll only see one or two pop ups all year, so just focus on grounders. Run them through that and batting practice and do that all year. Anything more advanced could be a waste.
