A few years since I last went, but I thought the Magna science adventure centre was good. www.visitmagna.co.uk/ It's Rotherham but easy enough to get to from the motorway Meadowhall junction.
You can visit this shop in Rotherham town centre, which might amuse for 15 minutes grimmandco.co.uk/ If you do want to visit, check the opening hours.
I doubt the rest of Rotherham would appeal though, so perhaps head into Sheffield, they are near enough.
though to be honest I'm struggling to think what else might be of interest to kids of that age around Sheffield, unless they are into architecture, art or walking/nature. You could probably walk round the nice bits of the town centre in 10 minutes. The Millenium museum and Winter Gardens (Sheffield town centre) often have special events over school holidays. Kelham Island museum a bit further out of the town centre.
Parking in the town centre is a right pain though, it might be better to use the park & ride at Meadowhall and get the tram in.
www.butterflyhouse.co.uk/ North Anston just off the A57 towards Worksop.
Perhaps a trip down one of the Peak District caves, the Blue John mine or Speedwell cavern, which are also fairly near Sheffield.