In keeping with the spirit of the title of this thread, I think you should make sure you visit the
BRITISH MUSEUM. It should be an easy sell to the family, and the Great Court can be a good place to take photos.
But after you've visited the museum, you'll probably fancy a rest and a cup of coffee,and therefore a visit to
Aperture Photographic is required. It's a wonderful coffee shop / camera shop in Museum Street, just south of the museum. Where else can you get a cup of Java and see a 300mm f/2 lens? (No, that's not a typo. They had a Nikon 300mm f/2 last year. £9000 if I recall correctly.)
And then you'll find yourself in a little cluster of camera shops:
- York Cameras in Bury Place
- Microglobe in Galen Place (off Bury Place)
- Jessops Classic Photographica in Great Russell Street
- Camera City in Little Russell Street
- The Classic Camera in Pied Bull Yard (off Bury Place)
Plus you're just around the corner from the Jessops flagship and the Jacobs flagship, which are opposite one another in New Oxford Street.
Incidentally, next time you're planning a "family outing", this is a useful resource -
www.ukcamera.com lists pretty much every camera shop in the UK, by town.