We went to Warwick castle last week; it is expensive but I thought they did things pretty well. DD enjoyed the Dragon tower thing but I thought it naff; she didn't want to go into the dungeon so that saved a bit. She's too old for the 'princess' crap The 'falcon' show was sodding great big eagles which I've never seen flown anywhere else ,the swordfighting and trebuchet are good. Something about climbing the spiral staircases while freezing knackered my legs though!
We also went to Ragley Hall - can't remember price, but apart from the usual house and gardens it has the best kids playground. There's really big stuff meant for over 12s (why do so many playgrounds not cater for young teens?)as well as loads of smaller equipment, and the multi-level maze.
(we were spending 3 nights in Stratford - the main events were the Tempest and Comedy of Errors. Having one 13yr old we get to do proper culture nowadays as well as having a playground connisseur
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Then en route back north Ironbridge - the year family pass is ~£65 but includes 10 sites which you can visit as many times as you want in a year and they punch it so that if you haven't done them all within the year you can do the ones you missed any time later - that's more generous than most.
On the way down, RAF museum - couple of quid to park and its FREE and really good. The interactive stuff is well designed and all actually works.
Someone mentioned Martin Mere - that's near us, and granny used to live near Slimbridge so we have WWT membership. Brilliant, we always enjoy it. There's kids stuff (good playground, craft, usually something like pond dipping) but proper wildlife too out on the meres. The canoe trail is quite fun too esp if you make the kids paddle
DD went to the Museum of Lancashire Life with school a few years ago and was underwhelmed - I'd heard they'd improved it, sounds like we should give it a go 