Itinerary advice for 11 days

Stay in Paris 5 days and see the sites there and include day trips to Versailles or Disney Land (if thats what the kids like)
Take the train to London from Paris that goes under the Channel. Stay in London 5 days see the sites maybe take a day trip to Stonhenge. Then back to Paris to end your trip.

Why not France for the entire trip? 11 days (10 nights I presume) is not enough to do all of France, much less two other countries.

It is helpful to plan in terms of nights: how many nights will you sleep in each place. Then you have a better picture of how many FULL days you have to see a place. 4 nights = 3 full days to tour. Every time you change locations you will lose at least 1/2 a day. AT LEAST 1/2 day by the time you pack, check out, go to the station, take the train, find your new hotel, unpack, get oriented. In the case of going to Switzerland from Paris, for example, it will be closer to a full day. Flying can save a little time, but with airport transfers it is not always much better.

So given that and assuming you have 10 nights, perhaps

4 nights/3 full days Paris

3 nights/2 full days Brussels

3 nights/2 full days Amsterdam - fly home from AMS

OR

4 nights/3 full days Paris

3 nights/2 full days Bath - take the EuroStar through the tunnel to London then on to Bath, ending your trip in London

4 nights/3 full days London - fly home from London

"We land in Paris and are planning to stay there for 3 days"

Oh yeah you should clarify whether or not you already have a round trip to Paris so we don't make suggestions about flying out of another city.

I do have round trip tickets from Paris but our flight home is from Paris to London to the U.S. so I assume I could just stay in London and skip the leg from Paris to London.
We arrive early in the morning June 16th and leave June 27th. I am thinking the suggestion of 5 days in France and five in and around London is probably best. I just want to cram it all in, though I know I can't and shouldn't.
Thanks so much for the input.

You can not skip the leg without telling the airline. Otherwise they will cancel your reservation. You have to contact them about that and then they may treat it as a change and charge a fee.

You can skip only the last leg. Otherwise they cancel your reservation. Once I flew from Prague to St.Petersburg and round trip was cheaper than one way. So I bought roundtrip and use it as one way. I did not need the ticket back to Prague because I was flying back to States from Moscow. That's what I meant you can skip the last leg when you don't need it. But anything before and they cancel all your trip.

First, plan to spend more time (perhaps half?) in Paris and do some day trips from there. Then perhaps one other destination and do day trips from there also. Moving around from place to place almost always takes more time than one anticipates, and you don't have enough time to "lose" much of it relocating. Secondly, considering the age of your sons, ask them where they would like to go and get them involved in the planning process. If they help plan it, it's less likely they will be unhappy campers during any part of the trip. Teenage boys that age are totally unpredictable so who knows what they'll come up with.

I'm sure they will have plenty of opportunities to return to Europe but probably not with me. Both finances and chronic illness make this trip a bit difficult for me but I wanted to do it before either of these factors got worse. I want to see them experience the eye-opening, mind-broadening effect of foreign travel first hand. I want to be able to show them everything. I'm going to follow the suggestion that we stay in Paris longer and then we'll head to London. I'll check with the airline before skipping the first leg of the flight. Thank you all so much for your help!

June
16. Arrive Paris (4N)
20. Eurostar to London (3N)
23. Fly to Amsterdam (3N)
BA2762 /dep LGW 16:05 /arr AMS 18:25
26. Thalys to Paris (1N)
27. Depart Paris

Depending on your flight time departing Paris, you could travel directly to CDG by train from Brussels even.

I like David's idea of putting Amsterdam into the mix.

Paris is a much more compact city, whereas London's attractions are spread out all over the place.
That said, I'd spend maybe one less day in Paris and add one more day to London.
If there is any possible way to reverse your flights and fly into London then fly out of Paris, you would save a considerable amount of money.

You will lose most of the first day when you land in either city, due to getting to your hotel and trying to get your bearings and maybe something to eat and a little nap.
If you have an early flight back home, you will lose about half a day.
It's good to realize how time flies when you're having fun...

You should look at this website, which explains everything you need to know about taking the Eurostar:
http://www.seat61.com/Europe-train-travel.htm
Due to security concerns, you should allow about one hour before your Eurostar train departs from Gare du Nord.

With all due respect, you are making some very large, important mistakes.

First, your idea of "skipping" the first leg of your return flight home will result in a very nasty, very expensive surprise: your tickets home will be canceled, gone, lost, poof. Then, you will have to buy new tickets home, and they will cost you a fortune. "Calling the airline" before doing this won't help. They sold you a ticket home from Paris. If you don't get on that flight in Paris, your ticket is worthless. You can check with the airline to see if you can change your flight home from Paris to London, but prepare to pay more than you expect (maybe a lot more - airline ticket prices follow no human logic) - it may or may not make sense.

Second, I agree with everyone urging you to limit your number of destinations. And you do not have "11 days". You have 10 days, at best. The day you arrive (even if it's in the morning) is going to be a groggy, jet-lagged blur (hope you sleep well on planes). Most people are not back to 100% on the day after they arrive (which is the real "day 1" of your trip), so plan an easy post-arrival day so you can ease into things.

Yes, it would have been more efficient to fly in to London, do a few days there, take the train to Paris, do the rest of your trip there, and fly home from Paris (you save a few bucks in taxes by NOT departing from London). If you can change your flights without getting whacked with a major price increase, that's a better way to do it (start in London, no language barrier, culturally easier to adjust). Day trips from Paris or London but...remember you only have 10 full days. You burn most of a day every time you change locations. You will enjoy your trip and get more out of it if you limit yourself to fewer destinations.

Good luck!

Ask your children to make a list of the things they want to do/see. We took a 16 and 15 year old to Paris for 5 days and it was about right. Then we drove up to Normandy - Mont Saint-Michel - Loire Valley - back to Paris for the last night by airport. If they want to experience 2 countries then Belgium would be the closest if you're driving.

Your sons are old enough to have some input; even if you decide on the cities, they can each plan a day for all of you. This will make them more participatory and make the trip more meaningful.

No data to prove it, but I think the sooner they start making plans, the more they will want to travel.