First Trip to London with 3 teens....15, 15, 17....HELPPPPP

I would hire a driver service to get five people with luggage from LHR to central London.
You will buy Oyster cards for Tube and bus transportation and add money to them on a machine in the Underground stations as needed. The Underground is easy to navigate and saves you from dealing with traffic. There are also transit passes for set amount of days in London once you decide your schedule you may prefer these to the Oyster card.
Buy your Eurostar train tickets, RT London to Paris to London way ahead of time for much better prices.
Use your ATM card as you do at home. Call your bank to notify them of both of your foreign travel locations so they don't block your card. Buy plug adaptors for the UK, and Europe two pin adaptors for Paris, to charge your devices. I always carry extra ones in case I leave one behind in a plug.
Buy entrance tickets online to sites you want to visit in London and Paris such as Churchill War Rooms, Westminster Abbey, Windsor Castle,Tower of London. In Paris you can buy a museum pass but they are good for three days so might not be cost effective. We split time in London and Paris with our young(11 and 13) grandchildren and our grown kids.. They loved London and didn't want to leave. They liked Paris but they loved London!.
Most of the museums in London are free and our grandkids liked the British Museum so much that it was hard to get them to leave.They also loved Fish and Chips inLondon and Baquette sandwiches and Nutella crepes in Paris.

Great advice above.

Public transportation in London - the Underground (Tube), buses, and some local rail - are operated by Transport for London. Visit their website and play with the journey planner once you have a trip in mind (from your B&B to the Tower of London, or from Victoria undeground station to the British Museum, etc.). As noted, you'll each buy an Oyster card. No need to buy the "Visitor Oyster" in advance, just buy 'em when you get there. The website is: https://tfl.gov.uk/

You must have some idea where to start because you've bought the plane tickets and booked the hotel. Take a deep breath, or three, and get your hands on a few guidebooks. Rick Steves, of course (hey, this is his website), and others such as Lonely Planet. Make a list of the things that each member of your family is interested in seeing/doing in London. Then start reading the guidebooks and refining the list.

These days, Google maps and the like are great resources to find the sights you want to see, in relation to each other and your hotel.

I've found - as have others - that a good way to plan your itinerary in London is to plan your daily schedule with geography in mind, visiting venues in the same area on the same day to avoid the hassle of long tube/bus trips in the middle of your sightseeing. (Don't ask me how I learned this the hard way because I shoulda known better. Okay, I'll fess up. I had to bug out early from a guided walk because I realized I had to get from down the river near Greenwich way back up to Westminster Palace to make it to a prebooked Parliament tour. Not a disaster but not fun either.)

Also, I have found - and others have too - that a good policy is to schedule no more than two "major" or "must see" things/places in a day. Those are the things that you absolutely will regret not seeing/doing, or venues that will take a bit of time to get through. Then depending on the time available you can fit in other things as time, interests, weather, and life's general unpredictability allow.

We have no idea what your family's "must sees" would be. You could be serious outdoor hikers and not interested in art museums, or a bunch of serious musicians, or railroad geeks, or diehard Beatles fans, or . . . anything else! So make some lists of what you'd like, and have fun planning. I love London and I'm sure you'll have a good time!

Where are you staying? I stay on Ebury St near Victoria Station and have found that taking the National Express Coach from Heathrow to the Victoria Coach Station is the easiest method for me. The driver loads the suitcases underneath and I plop down into a seat! Fare is 10GBP and it takes about an hour. Not sure if they have a kids fare.

If you are going to Paris you should book your Eurostar tickets now. You've probably already missed the cheapest fares and they will only get more expensive. I suppose you've already bought your airline tickets? It works well to go open jaw - in to London, home from Paris. Book at https://www.eurostar.com/us-en

You should get one of Rick's guidebooks. He covers a lot of the basics that you are asking about.

Many of the museums in London are free - National Gallery, British Museum and Victoria and Albert to name 3. You do need to pre-book for Churchill War Rooms.

Any interest in London Walks? www.walks.com

As you only have 10 days, I would advise against "hopping over to Paris." Not only will it cost a bundle, but you'll be eating up precious vacation time sitting in transportation vehicles, and you won't have enough time to do justice to Paris at all. BTW, is your stay actually 10 days on the ground, or are you going to be away from home for 10 days? If the latter, then your time on the ground on the other side of the Atlantic will be only 8 days because the day of arrival and day of departure don't count.

There is plenty to see and do in London, and there are endless nice day trips outside of London to choose from if you want a change of pace. In fact, if your goal in visiting Paris was to hear French spoken, you can go to one of the ferry ports on the south coast and encounter plenty of hotel and restaurant workers who are bilingual.

Good advice above, especially to read a guidebook or two. See what you can find in your library and buy a current edition of the one you like best. I'd recommend RS or Lonely Planet. Also find a lot of good sightseeing info under "Explore Europe" on this website.

I'd skip the "hop over to Paris" on this trip. It will cost much time and money, and Paris deserves much more than a day or two. Instead, take one or two day trips to places outside London that interest you -- Windsor, Canterbury, Oxford or Cambridge, Bath, Brighton, Salisbury and Stonehenge, etc.

Oyster cards will help with London transportation. A few adapters for your devices (not transformers unless one of the devices is a hairdryer, which is probably not worth the bulk and weight to bring along).

Maybe your teens can figure out a lot of this, along with the sights that interest them most. They'll have a better time if they're invested in the trip.

I respectfully disagree with suki.

With 3 strong teenagers to help you with luggage (and how much luggage do you have for 10 day tour anyway) it would be much better to buy your Oyster card in Heathrow and take the Piccadilly line. Use the TFL link mentioned above to find the best route to your exact address.

Not only is the tube much cheaper, but it is a part of the experience. As you go nearer to London it gets more "city-like" and less "airport-like".

Many of your questions are already answered on this website; look at the Explore Europe menu. Better still, turn your squad of young adults loose on the research. Then listen to what they find. They should be joining in the decisions, so they feel that they too have toured London -- with fewer cries of 'helpppp'.

If you are sure you want to see Paris even if it's just a day trip, Eurostar tickets go on sale 6 months prior to your travel date. That means for April, they have been on sale for two months and the inexpensive tickets go rapidly. Check out Eurostar.com. A day trip is possible by taking an early train over and a late train on your return to London. Of course you won't do Paris justice but you can do and see enough to whet your appetites for future trips to Paris. Good luck.

Join Historic Royal Palaces as a family to save money/time on some major attraction (Tower of London, Kensington Palace, Hampton Court to name a few.) As others have advised, a few days in Paris might not be practical. When you are in the Trafalgar Square area (you undoubtedly will be), consider eating at The Crypt at St Matin in the Fields (https://www.stmartin-in-the-fields.org/visit/cafe-in-the-crypt/). Fascinating place, great reasonably priced food, quick, and the teens will be amused. There is so much to see, and there is no way to do it all in ten days, or 10 months for that matter. Have the kids do some research, and then sit down together and see what everyone has on their "must-do" list. Plan those first, and then fill in the gaps based on what is in the areas where you will already be. Check that everyone has their walking shoes now, and makes great friends with them before they go. You dont want to be breaking them in there. Use your credit card for everything you can (the major ones generally have great exchange rates), and order a few hundred dollars worth of GBP's from your bank before you leave (usually takes about 3 day's if they dont have then on site).

Each teen should plan one day of the trip.

All these posts are amazing. I truly appreciate each and every one of you taking time out of your busy schedules to post information, advice, tips, etc. all very helpful and great tips!!!

Thank you,!
-Less Confused

Definitely get the teens to help planning ! We have taken all three of our kids to Europe ( all including London and Paris as well as other places ) for one on one visits , and the youngest was only 11 and all of them were REQUIRED to put in some research equity into getting a great free trip to Europe ! Each child was told to pick three sights they wanted to see in each major city we visited . This was easy even for the 11 yr old as how hard is it for them to google “ top ten sights “ etc . My then 13 yr old discovered the Catacombs in Paris , somewhere I’d never heard about until he found it ( and I personally had already been to Paris many times before ) , my daughter ( she was the 11 yr old ) wanted to visit the Halocaust Museum after reading Sarah’s Key , and my other son wanted to go to Thorpe Park ( hey it doesn’t always have to be a cultural experience when dealing with kids ) by letting them choose places it really negated any whining about being dragged through cathedrals etc lol

hey beanie665
yes it can seem so overwhelming and some posters here have given you good advice. what are the dynamics of your kids, boys girls both? like that you get them involved with research. let them look and pick out what they: really want, ok to miss.
withlocals.com has things to do. visitlondon.com, walks.com (beatles magical mystery tour or the beatles in my life for mom and dad, little venice within canals and houseboat living, royal london, portobello/notting hill markets, harry potter on location and film locations, street art, hello london) read up what's days they have what tours.
cafe in the crypt for lunch. (stmartin-in-the-fields.org)
royalparks.org.uk at regent's park they rent boats and pedalo, princess diana's memorial playground, peter pan's bronze statue
thamesrockets.com
matinee theatre show, afternoon tea (girlsafternoontea.co.uk, b-bakery.com, afternoonteaonline.co.uk)
jasons.co.uk
streetssensation.co.uk for street markets.
londonist.com or timeout.com search for best sunday roast lunch in pubs, come hungry. walk thru covent gardens, picadilly circus, trafalgar square an interesting array of "free" entertainment maybe with a hat/basket on ground for a donation. eat fish and chips, have a london gin cocktail, we did a gin tour, great time.
there is a lot to see and do in london, hopping paris is a no go and time consumming, plus expensive, 5 R/T tickets will cost you at least 600E not counting 2 hotels rooms for the family, that's my opinion but your vacation and $$$. take a day trip to brighton, beach and boardwalk, everyone will have a fun day.
london's a big and busy city all the time. when we went i swear i heard every language in the world there were people from all over the world. was there when the oakland raiders played football, team near where i live, regent's street was a mass in red white and blue, crazy, insane and sane people everywhere, and the pound was UGLY (1.73GBP) we had so much fun. this will keep you busy, pack light, the kids are in charge of their own bags, i'm sure there is a laundromat close by, just curious you mentioned B&B for 5 people?
aloha