If you don't have enough, then you need to meal plan and include d everything you will eat over the week breakfast, lunches, dinner, snacks.
We are a family of 3 (2adults, 1Ds15)This is a typical week for us
Breakfast - cereals, fruit / fruit juice
Lunches - salads during the week (cheese, ham, chicken, egg, tuna), fruit, cereal bar, yogurt/jelly, little pot of nuts. Weekend tend to be sandwich/soup/toast, crisps, cake.
Dinners - curry, spag bol, risotto, shepherds pie, fish and chips, grilled meat with oven roasted veg, fajitas, burgers, roast dinner. Icecream, rice pudding, fruit,
Snacks - fruit, biscuits, cereal bars, nuts, cheese, toast, crackers, raw veges.
Drinks - tea, coffee, hot chocolate, milk, squash,
the main meals are all pretty healthy, so we actually don't do too much in the way of snacks as we tend to stick to 3 meals a day. That means on the odd occasion we do them I'm pretty relaxed about it, the occassional biscuit / nutella sandwich is not going to do much harm.
I don't do individual meals for everyone, you either eat what I'm cooking or you go hungry. It stops any fussiness and waste of food.
Once you know what you are going to eat, then all you've got to decide is how much.
Alternatively, you could take a week or 2 and write down everything you actually eat as a family and that should give you a better idea of what and how much you need.