Throughout September 2008, children aged 2-11 go free at Blackpool Pleasure Beach when you purchase a full paying adult wristband (normal cost of child ticket, £20). Not sure whether it's book online only or whether it applies at the gate too. Online tickets must be bought at least 12 hours in advance.
The wristband also includes entry into one of the Pleasure Beach shows including their spectacular ice-skating show, "Hot Ice".
September might not be a convenient month for everyone, but it's not too bad considering that Blackpool's famous 6-mile stretch of Illuminations are currently running every night and there's Musical Firework Championships from North Pier at around 8.30pm every Friday during September.
For those who want to stay overnight, there's a Travelodge on the way into Blackpool, where rooms start at £39 per night, although you may be able to get cheaper at a local B&B.