Ok, I did my research and I still don't get it. We're a family of 4 with two kids - 11 & 9 and we're flying in to London at 5ish on a Wednesday and leaving at 1ish on Monday. I was going to go with an Oyster for the two adults and a child travelcard for the 11 year old, but now I'm thinking about the 2 4 1 offers. I definitely want to see the Tower and the Eye, so it seems we could save money if we did that. Would we be better off buying 7 day travel cards instead of the Oysters? Can we buy 1 day travel cards in advance, i.e. buy them on Wednesday for all days including monday? And do we or do we not need a photo?
Thanks for your help!