Travel Card

Travelcards and Oystercards are the same price wherever you buy them from in London, its only if you buy them outside London or locally in your own country with the visitors versions that you pay more.

The 2 for 1 promotion is only valid for any rail ticket issue by a rail company to London. There is a loophole whereby in Cerntral London you can purchase Travelcards from the ticket office of a rail station and these qualify for the 2 for 1 promotion sponsored by the rail companies.

All other Travelcards and all Oyster Cards are not valid for the 2 for 1 promotions.

The child ticketing starts for people under 16, anybody 16 or over is treated as an adult.
Kids under 11 travel free anyway, and kids between 11 and 15 its usually best to get an accompanied 1 Day Travelcard each day that costs 1 GBP for unlimited travel and you do not need any photo id. With Oyster you have to apply well in advance to get a special photo id card.

Hi! Small world. I'm also in WC, trying out the 2-1 eligible Travelcard, and traveling with my niece who is under 18.

As far as I can tell...the price is about the same (if not exact) for a paper card or an Oyster card.

You have to buy a 'rail' travel card (paper ticket..,.is the key...not Oyster 'plastic' card). to get the 2-1. Paper travel cards are available in 1,3 and 7 days. The confusion is that Oyster cards are also called travelcards and for 7 days.
So...bottom line (from what i have read)...is go to a train station (victoria,
Euston, St Pancras, Waterloo, and a few others others...are both tube and rail). You have to find the right 'ticket window (purchasing area) ...which should be the one selling rail tickets vs the one selling tube tix.), Just ask them for a PAPER travel card (1-3-7 day...whatever works).

I believe if you buy 7 days, you can do 2-1 attractions for the entire 7 days it's valid.
Before we go, we got on the tfl website to get my niece a (5 pound) photo ID so she can get half price purchase of the travel cards.....shes 17. But the TFL website tells you what you do (if you need to do something before you go, or if you can just do it there). We did it online, and will pick it up on arrival.

Worst case, if for some reason you get an Oyster that isn't supposed to be valid for the 2-1..try it anyway.

TFL website: http://www.tfl.gov.uk/

Good luck!!

One more thing...just be sure it's a rail pass...that has the rail symbol on it. But the travel card works the same as it would if you had a tube travel card. The 'symbol' is sort of like 'crows feet'. There is a sample here: upper left of the web site:
http://www.nationalrail.co.uk/

One bonus with the Oyster card is that you can register it online so if it is lost or stolen, you can get a new one. The paper travel card is a complete loss if you lose it.