With teenage boys you might consider heading north and spending a couple of nights at Saint-Vaast-la-Hogue. It's a pretty area on the east coast of the Cotentin peninsula. On the way there you could stop at Saint-Mère-Eglise, see the paratroopers in the stained glass windows and perhaps visit the museum there. At Saint-Vaast there are some decent harborfront restaurants and impressive old defensive towers designed by Vauban.
Using Saint-Vaast as a home base, you could make a day trip over to Cherbourg to see the largest submarine in the world accessible to the public: the retired French nuclear sub Le Redoubtable. It's hard to describe how large it seems up close, but it's big and comparable in size even to present-day nuclear subs. There's an excellent English-language recorded self-guided tour you carry with you as a handset during the visit, and you can go at your own pace.
At the same port area (short walk away) is a small museum dedicated to the Titanic, which stopped in Cherbourg before heading on to its fate in the Atlantic. It does a pretty good job (again, in English if you wish) setting the stage for what transpired with its voyage.
Other places to hit are Barfleur (a pretty, stone port town) and some interesting porphyritic geology (if your teens have any interest in that) along the coastline near the Gatteville lighthouse (phare de Gattevile). You'll see by looking at a map that there are some beaches available between Saint-Vaast and Cherbourg if that's an interest as well.
I'm a parent of former teens, if that helps. They got older, for some reason.
Edited to correct an oversight: at the same port area as Le Redoubtable and the Titanic museum is Cité de la Mer, a well-staged marine aquarium worth a visit. You can buy a combined ticket that covers all the attractions at a discount at some restaurants and hotels, and probably some tabacs as well. At Cité de la Mer also are various deep sea submersible vessels from over the years, including a replica of the submersible James Cameron used to visit the wreckage of the Titanic, so that might be of particular interest to teens given recent, tragic, events.