Jacket potatoes with help-yourself, mix-n-match fillings: grated cheese, broccoli, baked beans, peas, mushrooms, etc.
Rice, cooked, then with any of all of chopped carrot, peas, tomato, raisins, broccoli, etc, stirred in. You can call this risotto, or pilaff, depending on which you think will sound more attractive to the children.
The above with couscous if you have it.