Like others have said if you haven't already wrote down a budget with your ingoings and outgoings on it you need to do one now.
I did one a few years ago,when we were always skint although it felt like we shouldn't be and I was amazed how much money we were wasting each year without realizing.
It's made a huge difference we never live hand to mouth now and we both have savings which was something that was impossible before.
Have a look at any contracts you have,phone line,mobile,tv package,broadband,Insurances,gas and electric and see if you can get a reduction in what your paying even if your contract is far from up if you ring and say it's costing to much and you can get a better deal else where they will usually always offer you a reduction in your bills.
With the MOT on your car you don't have to use the garage that does your MOT for any repairs they say you need,you can shop around for somewhere cheaper or better still see if you have any friends or family that are good with repairs on cars.Knowing the right people has saved us thousands on repairs over the years.
Depending on how old your child is,how about a visit to the cinema at the weekend as a special treat.Lots of Cinemas offer special children's viewings now that cost between £1 and £3 a ticket each,take in your own sweets,popcorn and drinks that would save you a small fortune.
Maybe Mcdonalds afterwards for a children's meal each really cheap and they get a toy as well.
Have a look in charity shops(I've bought loads of brand new items,toys,books,clothes from our local charity shops for a few pounds at the most)if you have any cheap shops near you lots of them now stock brand name toys,books and stationary(we have a pound shop near us that's stocking toys that are selling for £10 in argos)ebay and facebook selling pages are also worth a look.
Card factory if you have one near you sell cards for 29p each.