We do not live in London, but visit from time to time, so 10-15y ago we bought an Oyster card for each member of the family. Our dc were all under 10 when we first bought the cards.
Are the Oyster cards the dc used still valid for them at 16+, or do they need to be replaced?
I can't find the answer on the TFL website, it just tells me to get Zip cards at £20 each.