I think that people may be being a bit harsh on the OP. it's really hard being on a very limited budget. I spend between £1 and £1.50 per person per day because it is all I have and I'm feeding MUCH, MUCH bigger kids than the OP (think 6ft3 17y/old and similar). DH works his socks off, but his wages are just too low and things like travel to work costs too high.
My kids are well fed, appropriate weights, plenty of energy. They eat plenty of fruit and veg, get enough calcium and protein and are never hungry. So it can be done.
A typical day would be something like -
porridge made with milk and some dried fruit
homemade soup with bread, a piece of fruit and a biscuit
mixed bean chilli with rice, milk jelly with fruit
or perhaps -
toast and peanut butter, fruit juice
tuna pasta salad, fruit
baked potatoes with cheese and beans, rice pudding and fruit
or -
cereal and milk,
hummus and carrot sandwiches with pepper and cucumber, biscuit
spag bol, (made with 250gms mince, carrots, celery, pepper, tomatoes, passata, garlic, herbs, tom puree), fruit, piece of chocolate
snacks would be biscuits, crisps, cereal, toast, fruit, cucumber sticks...
This week, I bought 750gms mince from Asda. it cost £3 and has made cottage pie for 4, spag bol for 4, pasta bake for 3, chilli for 4 and tonight I will make the left over chili into a cornbread topped pie for 4. I don't eat meat, so I have been eating things like roast mushrooms, beetroot salad, bean salad etc.
Believe me, if I had more money to spend then I would spend it, but you have to cut your cloth according to what you have. it's a grind having to account for every penny and not be able to just buy something that you fancy, but that's just life.