BF is excellent. Its a working farm which has extensive outdoor play areas, adventure playgrounds, live animal handling and (small) pony rides combined with a large indoor soft play area, cafe/bar and a shop. At Christmas they convert one of their barns into a grotto and its one of the best Santas we have ever seen. Its a good forty minute drive from South West London but if you go down the A3 and then head for Chessington World of Advertures (but keep going) the traffic is usually light.
Lets us know if you go and what you think. Link to their website is below.
http://www.bockettsfarm.co.uk/