I know I'm asking the impossible but... i'll be in London with 3 kids aged 9, 12 and 14. Dh will be working, we'll be based at a friend's house in Dulwich while they are borrowing our house. What is the best way to entertain them on a budget? I am a big fan of eating in places like chain store cafes rather than museums, bringing sandwiches if there is a park, that type of thing. Are there any recommendations for the best museums, markets etc.? Or rip offs to avoid?