My 4 year old twins are fabulous eaters, so your son would probably not like my recipes, but here is what my guys eat in a typical day.
1-2 bowls (fairly large) of cereal for breakfast. Cheerios, Kix, Kashi go lean crunch, shredded wheat, puffins, shredded spoonfuls, Annies cereals to name a few. Or about a cup to a cup and 1/2 of regular old oatmeal. No sugar, not the packets just regular oatmeal. I add milk to it instead of water, since my kids dont drink milk. and to the oatmeal I add about a quarter cup of frozen blueberries.
Snack. string cheese, 1/2 to a full apple, 6 crackers like wheat thins. or a granola bar, we like Kashi granola bars. Or a cup of plain yogurt with blueberries or whatever fresh fruit i have on hand. Sometimes i carry with me single serving containers of Horizon, Silk (soy) or goat milk yogurt for when we are on the go.
Lunch: a whole almond butter and fruit spread (no sugar homemade jam) sandwich, on whole grain bread. peas (sugar snap or regular), carrots or bell pepper strips. Small handful of Annies chedder bunny crackers. Hummus to dip veggies if I have it on hand.
Box of raisens for afternoon snack. Or a string cheese if they didnt have one earlier. Or a fruit different than earlier fruit.
Dinner: my kids eat it all. 4 Broccoli florettes, salmon with tomatoes and wilted spinach, 1/4 cup of brown rice. Or chicken breast with salad about 1 cup in measure. Salad would contain shredded carrot, avocado, onion, spinach, red leaf lettuce, walnuts or almonds, dried cranberries, tomatoes. They like all kinds of dressings but I mainly use vinegrette kinds.
Thats it, a typical day of meals for my boys. They are big eaters I know, but are not large kids. 41 inches I think and just hovering at 40 lbs. OH, and NO dessert, unless it is a special occasion.