London
Greenwich
Royal Observatory Greenwich -
Kids will want to stand with a foot on each side of 0 º longitude at the Prime Meridian. Everything on earth is measured east or west from this point. And, don't forget "Greenwich Mean Time" - the new year officially begins here at the Atomic Clock.
Tip: Royal Observatory, National Maritme Museum, Cutty Sark are included in the London Pass.
Along with the Royal Observatory is the National Maritime Museum. Ships, sailing and heroes like Lord Nelson ("England expects that every man will do his duty") are a big part of British history. The museum traces the history of ships from the 17th century up to the present, with tons of models, and hands-on exhibits.
Also, take a look around the Cutty Sark, a fast China clipper sailing ship, docked along the Thames. Kids can see what life was like at sea, play boxes with activities to borrow. Open year round.
Thames Barrier - Cruise down the Thames River to the Thames Barrier, movable gates that can be closed to protect London from flooding. It's one of those engineering marvels, the world's largest movable flood barrier. The Visitor's Centre has interactive exhibits and working models. Take the boat from Westminster Pier.