I think it is complicated, but reading the info at www.thetube.com it seems to me the best bet it to get a travel card when you arrive. Your two 15 year olds travelling with you gat acard for £1 each.

Problem with Oyster I see is getting refund of unused portions when you are in a hurry to catch your flight.

I'd suggest paying tube fair to London. Then get 3 X 1 day off peak travel cards (£5.30 adult)

see

tfl.gov.uk/assets/downloads/guide-to-fares-a…

and

tfl.gov.uk/assets/downloads/fares-and-ticket…

Travel in UK is expensive.

It is always a mistake to expect abroad to be just like NYC.

>>What am I missing??<< Plenty - but in your defence, it's not easy to find the info you need. :)

1. Forget Visitor Oystercards...like any tourist transport option it's marketed to gouge you.

2. Plain Oystercards are more felxible -with refundable deposits and unsued money - but probably not something I would bother with in your case.

3. Your kids will travel cheaply...Adults who have a Travelcard, which can be of any zonal combination, can buy child rate Off-Peak Day Travelcards (valid in all zones) at a reduced price of £1 for up to 4 children (aged 5-15 years inclusive), when they travel with them. (source: http://www.tfl.gov.uk/tickets/faresandtickets/oneand3daytickets/2908.aspx)

4. Buy single fare tube tickets to get you all from Heathrow to Kings Cross. £4 for you, £2 for each child.

5. Once in central London, buy off-peak daily travelcards - £5.30 for you, £1 for your kids. Off-peak is 9.30am onwards on weekdays and all day on weekends.

Are you returning back to Heathrow when you leave on the Sunday ?

In an earier post the OP wrote they are taking the Eurostar to Paris on the Sunday morning.

The subways you'll find in London are walkways under main roads; the transport system is the Underground, aka the Tube.

Visitor Oyster cards are poor value, so you may put it low on the list.

You way you'll use the Tube minimally, but you may be surprised how much you'll want to use London's public transport. The city is big, and after a number of hours of sightseeing, having a Travelcard will come in handy.

Travelcards allow unlimited use of the Tube, Docklands Light Railway and National Rail services in the paid-for zones, plus bus use in all zones. Pay As You Go on Oyster allows the same except for National Rail services - most of these services do not allow PAYG on Oyster, but you'll likely not be using the overground (rail) in any event.

PAYG offers a slightly better value as there is a daily cap on fares: 50p less than the equivalent one day Travelcard.

Your teens can travel for a pound each, as outlined above. But the Travelcards costing a pound each are good for off peak use only: you'll not be able to buy the cards until 0930 at LHR, but you will be able to use them to get from the airport to the city centre, then the rest of the day.

If you wish to buy one day Travelcards, a one day card for zones 1 - 6 (for your Friday arrival) will cost £13.80 if you buy it before 0930 the day of arrival, but only £7 if you buy it at 0930. Again, the card will be good for getting around all day.

With the cash single fare on the Tube £4 for adults and £2 for each child (no transfers of any kind are issued), waiting until 0930 will cut prices considerably.

Saturday? Weekends are off peak, so you may travel at any time, no need to wait until after 0930, so the teens can buy one day Travelcards for a pound each and you can buy a one day off peak card for zones 1 and 2 (all you'll need) for just £5.30.

A one day card for zones 1 and 2 covers a lot of London, and unlimited truly means unlimited - ride as much as you like.

In theory, then you could purchase four one day off peak cards (4 x £1), one off peak card for zones 1 - 6 (£7) and one off peak card for zones 1 and 2 (£5.30) ~> just £16.30, or about $US32. All you need do is wait at Heathrow until 0930 on Friday to take advantage of the lower fares. After that, London is open to you!

So Travellerplus has reduced your costs from US$75 to US$32, saving $45!

Well that is definitely good news...thanks so much for clarifying that!! But If I can't buy a card when we arrive, I'll have to just pay regular fare...we just can't sit around for three hours at the airport. Is that what you are suggesting...or did I misunderstand?

Heathrow is busy at 0620. It might take 30 minutes to get through passport control and another 10 - 20 minutes for bags to make their way from the plane to the belt. Depending on the airline with which you fly, you could have a walk of ten minutes from the airbridge to passport control; if you're flying with BA to T5, you may have the pleasure of seesawing escalators* to and from the people mover (a wee train) from T5B to T5A.

There's a potential that you'll not be ready to leave the airport until 0800 - 0830, depending on the airline with which you're travelling and the terminal building at which you arrive.

Should you want to leave before 0930, a Travelcard for zones 1 - 6 will cost £13.80 for you and £6.90 for each teen.

*Three long escalators down to the train, then three back up to passport control at T5A.

Okay I read through everything again, yes I see what you are saying...certainly a savings to wait, but I think I might go looney sitting around the airport that long!!!

Tell my if I am reading this right...

if I get a travel card, I'll need zone 1-6 cards to get to Kings Cross. If purchased at the airport before 9:30 - they will be peak cards, and will cost me, in pounds, 13.80 + 6.90 + 6.90. If purchased after 9:30, they will cost 7.00 + 2.00 + 2.00.

Sooooo about $55.00 (US) vs. $22.00. Okay - definitely not going with the Peak card!! Yikes!! Now...if I do single fare, then I'm looking at 4.00 2.00 + 2.00 = 8.00P. And then we could get an off-peak later...so I'd be out an extra 8P, or $16.

So it comes down to...is it worth $16 to me, to sit in the airport for 3 hours....right? Is that a fair analysis? Thanks everyone, for helpin' me out here!!

And for the poster above, no, I did not assume that London was going to be just like NYC...I was only talking about the subway - I did think that it would be similar. If I thought everything would be the same, there would be no point in going! :-)

Okay Travelerplus...I was not thinking about "getting out of the airport" time. That does makes sense...thanks for pointing that out. And thanks so much for taking the time to help a clueless mom! :-)

I've traveled to many many places, but never to London, and I am really looking forward to the experience!