Royal Observatory Greenwich and the National Maritime Museum (Greenwich) - Kids will want to stand with a foot on each side of 0 º longitude. Visit the Prime Meridian, the Royal Observatory Greenwich. 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.
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.
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.