Children who would never eat a usual large tomato love to puncture them with a fork and just eat them entirely in one bite. Hopefully, they'll chew them a little first. But that only brings back to me why more people don't eat salads. They're not interested in something that ships well. They want to eat something that tastes great.
Tomatoes are rich sources of vitamin C and lycopene, both potent anti-carcinogens.
But stews and soups count, and cooking tomatoes even seems to release more lycopene. Everybody has a different onion that they like, but you may find that some onions are just a little too strong for children's sensitive taste buds. That includes leeks, scallions, and shallots, and even garlic. Asparagus - Asparagus is usually lightly steamed before it's added to a salad. Remember, no matter how healthy the salad is, if it doesn't contain things people want to eat, they'll likely to just nibble on it and likely go on to whatever vat of saturated fats happens to be nearby.