patelp25,
You could spend all your time in England, Wales and Scotland, with a few days in Ireland. 11 and 8 will love the castles, Stonehenge, the countryside, London's war museum, the crown jewels and beefeaters, the London Eye. Beaches in the British Isles would be different from Calif. or Fla., but there is Brighton or Bournemouth.
You could also head to the Netherlands....Amsterdam's canals, windmills, the architecture, sitting with other travelers at a large restaurant table having a ristafel (sp?), even the Rembrandt museum, the bicycle culture (and traffic!). Also taking a tour to places like Volendam, seeing the Zuider Zee and learning how the pumping system and dikes work. All of these would be interesting to your kids, IMO.
We traveled to Europe when my two were 10 and 8, again when they were 20 and 18, and they went on their own after each finished college. In 2023 we all went again with our grandkids, to France, at 9 and 12. Kids can be more interested in things we think they would find boring.....art museums, churches, country markets. They can go to amusement parks at home. They might surprise you with what catches their imagination. (And, of course, in England, there is the Harry Potter connection.)
One thing they (kids and grandkids) always enjoyed...shopping at a grocery store and comparing what they find there to what we get at home...types of cereal, cookies, even produce. They liked to buy snacks that were different from what they got in the US. Have them look for peanut butter at a small country market.
Have a good time, whatever you decide. Amusez-vous bien!