You'll be in town when all the Christmas decorations and lights are up.
The Hyde Park Winterwonderland will be in full swing. Games, rides, food. Like a carnival. FREE entry.
Camden Lock Market
Definitely Tower of London. Then walk up to the glass covered Leadenhall market which abuts the futuristic looking Lloyds of London building.
The Horniman Museum.
Have lunch or diner in a pub like The Blackfriar.
Check TimeOut London online to see when and where Santa runs are scheduled.
Enjoy a Sunday roast.
If neither of you suffer a fear of heights, the Tower Bridge Experience.
Westminster Abbey. Take either a London Walks or Vergers Tour.
London Walks Jack the Ripper or Ghosts tour(s). www.walks.com
Imperial War Museum.
Can he ice skate? The rinks will be set up. One outside the National History Museum.
A Theatre performance of Wicked or Aladdin.
I'd opt for Bath.