We are taking one of the boats down the Thames to Greenwich and the maritime museum, but want a more speedy return. Will our 7 day travel cards work, or do we need to pay extra (don't know if it is limited to zone 1 or 2). What is the best way to return to the Knightsbridge area( and that tube stop) ? Is it the DLR? And can our 10 y.o. Still travel for free on that route?