Science museum is free and lots of hands on things that they can do.
Woking now has a cheap travelodge with parking over the road from the station so although you would have to get a fast train into Waterloo it may work out not so expensive IYSWIM. May depend where you are travelling from though of course!
We are a family of 5 myself and dh, dd1 (6), dd2 (4) ds (9m).
Dd1 is 7 in january and we would love to take the family to london for the weekend as i know she would love this. We are thinking of driving so would love hotel recommendations with rooms big enough for us and free/cheap parking and close enough to a tube station so if its a bit rainy we dont get soaked.
We definately want to go to buckingham palace but would like other ideas of what to do whilst we are there. I would love to go to a show for children but not sure if there will be anything that we can take ds along to. Tia x