I am wanting a suitable venue for my boys' birthdays. One will be aged 7 and the other 3. Any recommendations please. Prices etc.

http://www.brewersfayre.co.uk/About/kids.asp

Kids love this place, depending on where you are in Sheffield the one I know of is on the A61 at Tankersley

Besides Brewsters,their is a new playcentre at Elsecar heritage centre.All nice and clean,hot or cold food,good carers who basically do everything for you,loads of seats for adults and lovely cappucinos!Approx.£7 per child but includes everything!
My twinnies had a party there and they had a great time and all the parents were impressed too!
There's also Magna and the Butterfly place at North Anston if you fancy something different!
oh....and Sheffield ski village [but that's mainly for big ones!]
Wacky warehouse do parties too!There's one at Brampton!:D