Thought it might be worth starting a thread for ways to pass the time, hopefully without spending a lot of money, in the school holidays.
Events at Cusworth Hall There are lots of events here that cost £1 per child and free for accompanying adult. They are having themes like The Secret Garden and Under the Sea.
Events at Doncaster Museum and Art Gallery These events seem to be tailored to 8-12 year olds but at half time they let DS (age 4) join in anyway.
There's the Town Field's Gala on 14th July and it's also the Classic Car Show at the School for the Deaf on the same day.
The Aircraft Museam behind the Vue Cinema at Lakeside is having a couple of open days. Sunday 21st July is helicopter preservation day and on 22nd July if you bring proof to show you are a Doncaster resident then you get free entry. I think there's another day in August as well.
The Dome are running some free clubs for children aged 4-17 who need to lose weight but I think you need to book in advance.