I agree with Linda Kelly about Warwick - plenty of space to run around and activities such as circus skills to keep younger ones amused. We have been taking Maddie (now 8) for a while now and she loves it. Whitby is also good and if you go to either of these this year we are there so they could amuse each other. I wouldn't go as far as letting Maddie off on her own around Whitby but there are lots of childrens events that are well supervised and give you a couple of hours to do your own thing - there are also family concerts and ceilidhs held early evenings which cater for children and don't mind as much if they are unsettled!
(You should have seen the Selbys on their walkie talkies giving their barbeque orders 15ft apart on Monday!!!!!!!)