Seven-year-olds have not developed all their tastes yet, but they can get in the habit of liking vegetables through introduction of rules like "at least two bites." You might also add fresh or canned fruit to your meals. I encourage you and your partner along with everyone else in the family to discuss how important vegetables are and the rules that will govern meals. Besides the "at least one bite" rule, another rule might be that there will be no desserts, snacks, etc. for anyone who doesn't eat sufficiently at the meal. Going hungry for a while or even overnight usually works wonders for the appetite of a seven-year-old.
Stepson Won't Eat Vegetables
Middle School Expert Advice from Connie Collins