Hi OP, I haven't read the whole thread so apologies if I'm repeating any tips!
First of all make a list of all of your outgoings and income. Check if you are entitled to any benefits and make sure you claim everything you are entitled to. On the outgoings, look at each one individually and search online to see if you can get a better deal elsewhere. It seems like a hassle, but if you do it after the kids are in bed it won't take too long!
I really recommend joining the money saving expert site, there is excellent advice on there and the posters are amazing and so helpful!
I find meal planning helps massively as I only buy what I need and I'm not wasting food. I do buy things when they are on offer e.g. toilet rolls (I never pay full price!), meat (keep it in the freezer), bread (again keep it in the freezer).
Don't necessarily buy your toiletries and cleaning products from the big supermarkets, I find Wilkinsons and Poundland have great offers and this has saved me money.
If you can get to a local market, do as the fruit and veg is cheaper than the supermarket, although I do find it doesn't last as long.
Also if you have any Indian or Chinese supermarkets near you, they are a lot cheaper than the big supermarkets and often have much bigger packs of things such as rice, lentils and spices.
Personally I avoid browsing in clothes shops so I don't want what I can't see! It's horrible not being able to buy something you want, so I avoid avoid avoid!
Surestart Centres are great as they are usually free and mine caters for ages 0-5 years. We have 3 parks within walking distance, so I usually take my baby to the park as it's free and he enjoys watching the bigger kids playing. My local cinema has a kids screening at 10am on Sundays which is £1 per ticket, I think this is brilliant value, so worth looking into for your kids as a (monthly?) treat. Arrange play dates with your children's friends as this will be as good as a day out, they can entertain each other for free!
I can't think of anything else at the moment, but good luck to you!