OK, so breakfast first. Breakfast for kids should have protein and fats, so foods like cheese, eggs, and yogurt are the way to go. Sour cream is good. Beans are also good. It sounds like you're in the southwest maybe, in which case something like huevos rancheros would be a great combination! A ham and cheese omelette with a dollop of sour cream would be a great start to the morning. Oatmeal made with whole milk, while carbs, is slow release, so combined with some protein it's a good breakfast option. Full fat yogurt has lots of calcium so is a good thing as well.
There are plenty of high-fat snacks out there, but they are usually junk food and therefore full of salt and artificial ingredients so I'd steer clear if you can. Cheese is a good snack, but avoid processed cheese and just put slices of the real thing in a small container. Unsalted nuts and seeds are great healthy snacks, and you can add some dried fruit and maybe a few m&ms to make a tasty trail mix. Yogurt pots are quick and easy to deploy, but watch out for sugar levels as some have ridiculous amounts in them.