Stanwick Lakes are fantastic and free- other than parking. Same applies to Emberton Park (Nr Olney). Both are outdoor, take your own picnic and warm clothes to get messy in but great fun. Enjoy!
I get to visit my grandchildren every 6 weeks or so in the Bedford/Milton Keynes area. I am not familiar with the area - any suggestions for a nice day out. I have done Woburn Safari park and Whipsnade but want something simpler. The children love soft play but they do that with their Dad so I would like to do something different.