Wraps or pitta bread with shredded ham and salad
Baked potatoes with chipolatas/bolognese/leftover casserole etc
Potato wedges with baked tomatoes & mushrooms
Shepherds Pie (mash the potato with soya milk or soya margarine, such as Pure).
Homemade pizza (or buy the bases) spread with tomato paste and add... tomatoes, peppers, ham, pineapple, sausage, pepperoni, mushrooms etc.
Tomato or minestrone soup with crusty bread.
And very good for children with multiple allergies is to give them pick n mix plates. Ham, salami, chorizo, weirdy German sausages from the deli, cold roast meat, olives, sliced raw veg & fruit, crackers, different breads, rice, pasta, quinoa, couscous (keep trying!), crisps etc and let them try as wide a range of things as possible.