I'm bringing my 2 kids to the UK in October and the last few days of our stay will be in London. We're staying really centrally but will want to get out and about on the tube and the buses. Last time we were over they were 10 and so travel was free. Now they are 13. So can anyone recommend my course of action for getting them discounted fairs? The zip card or a young person discount on their Oyster card or something else?