If you are visiting London with children between 11 and 15 years of age, traveling around the city can be made much simpler by purchasing Visitor Oyster Cards. Adult cards can be purchased from several countries before you even leave home, and once you arrive in London, you can ask a Transport for London (TfL) staff member to apply a Young Visitor discount to your child's card. You can buy a regular (non-Visitor) Oyster Card at Heathrow, and use either type of Oyster Card to get to central London from Heathrow and Gatwick airports (although not Luton or Stanstead).
What is an Oyster Card?
An Oyster Card is a plastic ticket with the shape, size, and function of a smart card. Like a smart card, you put money on the card and as you travel, the charges that you would normally pay in cash are deducted. Once purchased, the Oyster card covers all mass forms of transportation in London, the Underground (Tube), Transport for London (TfL) Rail and most National Rail lines in London, London Overground, London Buses, and Dockland Light Rail (DLR). It can be purchased on a daily or weekly basis; it can be used at any time of the day and covers attractions across all London, zones 1-9.
The Visitor Oyster card costs £5 to activate and then you choose how much credit you want to add to it in £5 increments up to £50. If you run out of money, you can top it up and use it again: at the end of your trip, you can get back the unused credit. In many cases, using a card to purchase a ticket is significantly cheaper than cash. In addition, the daily rate has a "cap" amount, and after you've met that cap or made your third journey in a day, you travel free for the remainder of that day. A Visitor Oyster card also comes with several special offers and discounts in restaurants, shops, and entertainment venues.
Children and Oysters
You don't need an Oyster card for young children. In London, children under 11 travel free on buses and tram lines, and on the Tube, DLR, London Overground, Tfl Rail and some National Rail, up to four children under 11 travel free if they are with a fare-paying adult. Buying a separate Oyster Card for your child aged 11-15 may be convenient because the Young Visitor discount is half the adult rate pay-as-you-go discount.
When you're ready to leave London, you can get unspent credit back, keep it for your next trip, or give the card to a friend to use.
Paper Travel Cards
If you don't want to go the smart card route, you can elect for a Travelcard, a paper ticket you can buy from a ticket machine at any London Underground station. A travelcard is a flat-rate ticket that covers all of your travel for one day or one week or longer. This means you pay a flat rate for that day/week, etc.
The paper Travelcard covers travel by tube, bus, and London Overground trains (local trains); travel is discounted, but there are no special offers and the money is not refunded. They are best used for large group travel. These tickets feed into the barriers at the tube stations and pop out again.