If your are headed for Edinburgh and Scotland add Dynamic Earth to the sites you can see there. It's great fun and full of information for kids about geology, biology and Scotland. Also, the castle in St. Andrews had amazing tunnels from when people tried to leave and/or get in by mining. Go to www.visitscotland.com and click on the visitor guide, things to see and do and then find families down in the lower right. All sorts of ideas are there. I bet there are similar sites for England, Ireland, Wales. You might have to check by city for continental ideas, but with a little surfing it's amazing what you find out.
Pam