If you're going on a family day out and you've only got two days to spend in London, then we've got a couple of example itineraries to help you get the best out of it -- londondrum.com/planner/two-days-with-ki ... h-kids.php
Here is idea number two..
Take your kid to London's biggest toy store -- Hamleys. Then try Ripley's Believe It Or Not!. Follow that up with a meal at the Rainforest Cafe, before catching a movie in Leicester Square. You next day begins at the Princess Diana Memorial Playground, then hire a peddle boat on the Serpentine, and finish with an afternoon at the Natural History Museum or Science Museum.