This will get worse with age. Much , much worse. Boys are dumpster trucks.
I have DS16, and DS13 - and they are like a mad hoard of locusts. Add a farmer to the mix ( DH) and if I don't get creative with cooking we spend a fortune on food. And when their friends come over? Oh Lord help me.
It's mental the amount of food they put away, and DS16 is skinny and tall(6 ft 1), DS13 is sporty and muscular and he is getting ready to grow - so cannot stop eating. He is going to be a huge man (size 12 shoes already) - it's like watching a German shepherd puppy or a wolfhound.
I've taken to making a huge pasta bake with veg each week and leave it in the fridge, as an "snack option". Or a brown fried rice Mexican style with black beans etc or homemade baked beans with toast. That's for after school. I always have lots of home-made sausage rolls with heaps of veggies blended through the mince in the freezer they can reheat. Otherwise they eat all the bread in toasted sandwiches in one afternoon.
I make weekly piles of protein balls - with a variety of nuts, dates, dried fruits, nutmeals, cacao, coconut oil etc, plus similar raw food bars for snacks, plus smoothies with protein additives etc and they have learned how to make a variety of those.
I've had to start dropping meat 3-4 nights a week as they just eat too much of it, and the price is bad news - so vegetarian nachos with lentils, vego chilli, big falafel wraps and things like that feature.
With meat , I do massive sausage casseroles with vegetables with mashed potato/sweet potato, or a variety of pastas/rice dishes and big salads with multiple ingredients, ramen's and pho noodle style bowls.
We no longer buy cereal other than Weetbix or porridge, and there are no biscuits or sweets in our house - they just inhale them. Costs too much.
School lunches are usually left overs, yoghurts and fruit, with slices of brown bread and cheese.
Both eat more than my DH and he's a martial artist as well as a farmer so he's no shy on the appetite stakes, and it is definitely about portion size. Even at 8 - 4 fish fingers would've been nothing for either of them. I'd up your portion sizes at meal times.
Good luck. Boys are evil with food.