London travel pass suggestion please

none of those

If you have a contactless card - debit or credit, but credit can be safer - just use that. Tap to enter and tap to get out and it will calculate the cheapest fare for each trip.

London Euston by train to Watford Junction for the free bus to Warner Brothers Harry Potter Studio, train takes about 20 minutes.

I don't get why you are staying at the airport for HP, Paris or Oxford. If you were near Euston or Kings Cross or anywhere near a Tube (the tube is slang for London Underground - they are like subway trains but much better, main line train stations like St Pancras, Euston, Paddington, etc., are for normal trains)

Keep asking questions...

Brit Rail is way overkill for what you are doing

if you use a contactless card you will pay the same fares as with an Oyster - but you don't have to spend all the money and time to buy the non-refundable Oyster (Seven Pounds non-refundable to buy) and then put on money you may not use. Just tap the card or your phone or your watch...

Firstly staying at Heathrow makes no sense for your trip. To get to the Harry Potter studios will be much easier from a London hotel, as will getting the Eurostar obviously. Fast trains to Oxford leave from Paddington station - it’s more convoluted from Heathrow.

If you were to stay at a hotel in the Euston/St Pancras/King’s Cross area (all close together) you will be able to walk to the train to Watford for Harry Potter and St Pancras for Eurostar. Then a short tube or bus ride to Paddington for Oxford.

You can take the tube from Heathrow straight to King’s Cross/St Pancras.

For fares just use a contactless card or phone or watch pay to tap in and out - no need for any type of ticket or card. The system will calculate the cheapest total cost per day. How old is the youth? That matters within and without London.

I don’t know what the Britrail London plus pass covers. If it is all travel within London and out to Watford and to Oxford then it might just make sense, probably overpaying but might be worth it for convenience.

Why two consecutive trips to Oxford?

Listen to Nigel.

He used to work for a train company. Very knowledgeable.

Difference between a tube/underground train is nill.

The London Underground is also called the Tube.

echo all the above

Don't stay at Heathrow

Use a contactless credit card to pay as you go

planning to stay at a hotel near LHR so it’s easy to go around.

This is a truly terrible idea. It will not make anything easy it will just add a long back and forth commute to what you want to see and where you can get trains to where you want to go.

. If it is all travel within London

My understanding is that Britpass doesn’t include tube, buses or Overground.

If you were staying at Heathrow and going to Watford Junction for Harry Potter it makes no sense to go by train via Central London.

You would take the hourly rail air link bus #RA3 in 45 minutes or the hourly Green Line #724 bus in 55 minutes.

Both are well faster than the train via Central London and the #724 bus costs just £3 each way. The Rail air bus costs £16.50 return, the train costs £9 each way off peak or £12.50 each way.

There are rail routes from Heathrow to Watford Junction avoiding Central London for £2.20 or £3.40 each way, but they are too complicated for a first time visitor.

To Oxford from Heathrow the direct bus every 20 minutes is by far the cheapest option, and easier than 1 or 2 changes on the train. It is also as fast as the train and puts you in Central Oxford.

Britpass doesn’t include tube, buses or Overground.

Britrail includes the Heathrow Express, the Elizabeth Line and Overground (but not tube or buses)- all those lines are part of the National Rail network. But financially it would still not work out regardless.

So, you're not actually planning to go to London except to take the train to Paris? I would rethink the whole trip because that seems like a ton of unnecessary travel and annoyance.

In any case, I recommend checking out London during your trip to London. It's worth seeing.

Thanks all for the helpful suggestions . Let me clarify and expand on a couple of things —
1) This 4 day July trip will be our 2nd leg in London this summer. Our first leg at London is for 2 days in May —- when we will explore London. Visiting India in between these 2 legs
2) Main purpose of second leg is — Harry Potter Studio visit, Paris visit and exploring/dropping off my daughter at Oxford. The reason for leaning towards staying near Heathrow is that my daughter and I will have 3 large suitcases and I assume that an airport hotel will allow us to store 2 of them , instead of us carrying them on the tube, to Paddington or Kings Cross (if we stay there).

just to clarify - you will be at the same Heathrow hotel both arriving with your two days in London and then for your 4 days near London and in Paris, then before you fly home? And during the two periods when you aren't in England you want the hotel to keep your luggage? If I'm right, have you discussed this with them? I ask because "and I assume that an airport hotel will allow us to store 2 of them" sounds like you're assuming without certainty...