Austria is great (I'm biased though as I live there). Easy cheap access with ryanair. Have a look at www.farmholidays.com and go for the link that mentions childrens holidays. You can go for self catering, B&B or half board. Choose a farm with 4 "flowers" (stars) and you won't be disappointed. If you have a little more to spend look at www.kinderhotels.com they all specialise in providing childrens activities etc.