Things to do in London with kids for free or cheap

How did it go??! I took my two daughters to london last month and we had a great time! They grew up between Paris and london but haven't been in london in 3 years so it was the right time to take them back! We went to the Aquarium after almost an hour queue we got in and were blown away! Its great fun better than parisian one Then we went to london dungeon they love horror things love it was a bit expensive but they loved it The day after we went to the brittish Museum and the Karl marx cemetery and in the evening I took them to the theatre I tried to find some cheap tickets in leicester square but they were running out, they adviced me to take them on Best London Musicals for Young Children and it was a great deal We had 3 tickets for the lion king for 15£ each instead of more than 30 pounds!