I spend about 350 a month on two adults and two children. They are both greedy and eat as much as an adult between them, and are both in nappies.
I don't buy poor quality stuff - we get organic bread and milk, and organic jam (because it's made with real sugar and not glucose-fructose syrup), I also buy fair trade coffee tea and drinking chocolate.
But I do buy a lot of own-brand and value-brand stuff. Value brand fruit and vegetables are often just smaller or slightly strange in shape. Value brand butter and flour is normal butter and flour in horrible packaging! I do have to be careful and read labels - the value pasta sauce had cornflour in it and tasted horrible, for example. But mostly they are fine - especially if you don't buy the packaged ready made stuff but get the raw ingredients.
Which brings me to the other thing - I cook a lot from scratch. I enjoy it, so it's not too much of a chore - except when small children are under my feet whining.
We also don't smoke, and drink very little alcohol, which really helps the budget.
I'd rather spend more and have more treats, but we're pulling in the reins a bit at the moment to blow on our holiday.