It's not easy. Think of the adage "needs before wants." Think back to year 9 commerce where we learn't that our basic needs: food, shelter and clothing need to be taken into consideration first. Priority of funds in the family budget should be allocated as follows:
Clothing - kids and then adults
School expenses: excursions, fees and stationery etc
The odd treat
Kids pocket money for helping out around the home...etc
Pass down clothing and shoes that are still in good condition. Kids grow so fast that many items of clothing are barely used before they have moved onto the next size. Friends and family always do clothing clear outs and you could ask if they could offer it to you to browse through before they send it to Good Sammies. Schools often have second hand shops which re sell uniforms for a heavily discounted price. And for yourself, why not hold a clothes swapping party with a group of friends.
Not everyone has the outlay to by in bulk but you could join with neighbours in a similar position and have a 'kitty' which would give you more spending power. Go for the things you know you'll NEED (not just want) such as toilet rolls and soap.
At the moment, one of our local supermarkets has a slogan: 'Feed a family of four for $15' - and I've been doing that for considerably less for years !
The knack is to look at your whole budget. I know this sounds obvious but many people spend on things which could have ben acquired more cheaply, or not at all, leaving more for food.
Look at vegetables first and creative ways of making cheap meals. If you're not vegetarian, cut down on meats. Never throw anything away. Use wholefoods rather than refined flour and sugars.
One of my families favourites is fried rice. Cook a pan of rice, drain and leave to dry (I usually do it the day before) add a finely chopped onion and a grated carrot. Heat a little ooil in a pan and add any spice you prefer. Toss the rice and veg into the pan and fry vigorously. In the last two minutes, beat up an egg (or two depending on how many you're feeding) and drizzle into the hot rice, stirring all the time. Served with salad if you have it, a little grated cheese (dairy is very expensive here and may be where you live so that's a rare treat). Brown rice is not only slightly more nutritious but less is more filling for hungry kids.