my children are a bit younger (nearly 2 and 4.7) but with us all eating 3 meals a day at home, we spend about £80 a week, including occasional nappies/wipes/laundry stuff.
Snacks tend to be stuff I've baked, or stuff that's on offer that week. Both children like dried fruit a lot, and any biscuits really. Our normal shop for food will be (e.g.) a small chicken, to do 2 meals, large bag of potatoes, bag of rice, bag or two of pasta. veg will be what's on offer - this week, green beans, carrots, asparagus, broccolli, and some baby corn. other than chicken, meat is bought in the 3 for £10 deal (sainsburys), so might be sausages, pork loin chops, chicken fillets. fruit is bananas (loads thereof!), apples, and satsumas. DH has granola for breakfast, I have a handful of it with a yoghurt, DCs have some godawful cereals and a banana. 12 eggs will do us a week, too. lunch stuff is a sandwich (with a filling or combo from: cheese/ham/peanut butter/jam/cream cheese/marmite/boiled egg), piece of fruit, and maybe some crisps if I've bought them that week.
I do cook from scratch a lot, but we will have the odd pre-prepared meal - tonight is chicken kiev with new potatoes. Tomorrow is a late one, so the kids and DH are having some frozen pizza as a treat, and I'll make myself an omelette.
I'd get value biscuits and crisps if I were you - it's worth trying different value products, and seeing which are actually good. for example, sainsburys value hummus is the best I've tried, and their basics bananas are fine too. basics apples tend to be so sour we can't eat them, so we no longer buy them.
we also don't drink fruit juice, so just have sugar free squash, but I think that keeps costs down too. do you have any branded colas or fruit juices? could be an idea to try non-branded ones?