Omelettes, tortillas, fritatta cut into slices, eggy bread fingers or french toast (often goes down well with little ones).
Different types of bread - bagels, wraps, muffins, subs, croissants - with fillings?
Mini pizzas made with muffins, bagels or rolls, tomato paste/passata, grated cheese and whatever toppings the kids will eat (get them to help making them).
Soup? Homemade chicken or veggie soups are super easy to make and healthy.
Jacket potatoes/sweet potatoes with whatever fillings the kids like.
I often make 'picnic plates' - slices of cold meat, cheese, some sort of crackers/rice cakes/oatcakes, pieces of fruit. Good for summer, as you can bring with you to the park or out into the garden. My 4 yr old DS loves this.