London again..(sorry)

TheBanker

Have a look here for special offers - 2 for 1 admission to attractions when you travel by train: http://www.daysoutguide.co.uk/2for1-london

I'd also suggest looking at London buses to get around. They're cheaper than the tube, I think they're easier with kids and you get a much better view of London from the top deck. It's like going on the official tour bus but you save £20.

Blackdog

Here are a couple of free museums to go to which are great for kids:
Museum of London at the Barbican
Horniman Museum in south London


Have fun!

bargainbetty

Go to the nearest mainline station and buy a single ticket to the nearest station. Then grab a 2-4-1 by train leaflet and use the ticket to buy tickets to the Tower of London, Churchill's War Rooms, tours, special exhibits etc. Have a look online, it's got a variety of deals.

I second the Natural History and Science Museums - I took two nine year olds there in August and had to practically drag them out. Also, take a bag of non-perishable foods for snacks (crisps, pasta pots etc) and a travel kettle. You'll save a bit on suppers. If you get a room with a fridge, use a local supermarket to get stuff for pack-up lunches to save a bit more.

Voucher sites often do deals for meals for adults (Amazon local are good) and if you visit Brick Lane, you can haggle a curry dinner with starters, mains, rice and naan for £10 per head for the adults, with a couple of drinks. Cheap deals for kids too. Very lovely!