We didn't go to the tower of London or Madame Tussauds and we didn't eat fish & chips(I wanted to but A, just didn't find time to cram it in and B, simply forgot) . We didn't go on a sightseeing bus or sightseeing tour of any kind. We didn't go on the London eye.
What we did do though was show our sons where we used to live and the parks and museums and places we used to visit as Londoners.
And of course we took them to the seven floors of toys that is Hamley's Toy Shop. And took them on loads of double decker buses and tubes, which they loved and to several adventure playgrounds which they also loved!