Mother-Son Paris trip!

You only have 5 days to see/do anything. Stay in Paris, for the sake of your son on his first visit. Save overnight side trips for another time...

I agree with Jojo. Five and a half days in Paris is not long, you will run out of time to do all you want as it is. Don’t forget there are great day trips as well for fascinating French history… Vaux-le-Vicomte, Fontainebleau, Versailles, just to name a few.
Normandy and D-Day sites, plus touring, needs a minimum of 3 nights, and more is much better.

Took my son when he was 17 and it was wonderful. He fell in love with the Louvre so.we spent two full ways there. One day Eiffel Tower at night. Walked large portion of Champs de Elysee. Up to top of Arch de Triumphe. He loved Sacre Coer more than Notre Dame mainly because of the view. Went to Versailles which did not impress him so much mostly due to crowded areas. Mostly he loved just walking around Paris. We did not go to Catacombs which we should have. I had rented a car and we did go Strasbourg which he liked due to the French-German mix. He really enjoyed time in the cathedral. On the way we stopped in St. Avoid which is location of the largest US cemetery of our WWII dead in Europe. We are both glad we did that as he said it really put history in perspective. it was very sobering. Then we went to Dauchau another terrible sobering day. Those two days were in his view the best and yet the most unpleasant parts of the trip. Wonderful for you two we were there full week not counting travel days. You will really only have five and half days because your flight home will probably leave Saturday morning. Sunday will only be a half day due to arrival, jet lag etc. You could probably have maybe four days just in Paris and maybe a one day tour to Normandy and skip Strasburg. Good luck and enjoy time with your son I really really did! We traveled together a lot and this was one of our favorite trips. He loved Paris.

While I would normally say that 5.5 days are better spent in Paris alone (+Versailles), you could do a day trip to Strasbourg if your son really wants to. It is perfectly doable, easier than a day trip to Normandy (train is faster, no tour needed). And you'd still have 4.5 days in Paris, which isn't bad.

If I was traveling with you, I would say stay in Paris. However, if my son was going I would encourage one day trip. I am glad I went to Versailles, but I wouldn't take my son there. (He is 25, not 15 but it wouldn't be his thing)

I love traveling with my son. Have a great time!
I recommend the Atelier des Lumieres.

Every son is different. My son loved Versailles at 11 yrs old and still does now at 32. We were just there again last week. The history of it is amazing.

My son fell in love with Paris from the first time i took him there at 11 yo. The métro, the Seine, the boats, the museums, cafés, bakeries, parks, Invalides (military museum), crèpe stands, the ET, ND, the Arc de Triomphe. Everything. He also loves other parts of France, in particular Normandy. My dad landed on Omaha Beach during the Invasion so it’s near and dear to our hearts. We’ve been 7+ times but never for less than a week. It needs, and deserves, time to see and absorb.

As a (retired) history professor, this so warms my heart! I would suggest drilling in a little deeper to his history interests. Even at that age, "history buff" might mean different things. He might love medieval knights and castles, but roll his eyes at tanks and airplanes. Or vice-versa. See where his interests lie and then take it from there. For example, if he's into Game of Thrones, Lord of the Rings, etc. (along with his history interest) I would definitely try to make Mont St. Michelle work along with a visit to the Cluny to see the Unicorn Tapestries. If he's more of a The Tudors and The Great fan, skip that and head to Versailles.

https://www.musee-armee.fr/en/your-visit/museum-spaces/musee-de-lordre-de-la-liberation.html

https://www.musee-armee.fr/en/your-visit/museum-spaces/musee-de-lordre-de-la-liberation.html

There are walking tours offered to see Paris sites from WW2 but there aren't a lot of sights. The liberation was mostly a guerrilla street action, now marked mostly by old bullet holes in older buildings. The context depends on the guide's story-telling knack.

The two links above are for more substantial museums. The fighting and the subsquent victory parade can be seen at the former. The latter, fairly new, describes the actions of the Underground and several of its heroes, with lots of films and photos and a section (at least last spring) on female war photographers. Taking it all in demands at least an hour and deserves to be better known.

If you go to the Musée de l’Armée, realize their version of the Liberation of France in WWII is very biased. According to them, de Gaulle liberated France. Still a good museum though, and it covers much more than WWII.
It has Napoleon’s actual horse, and a lot of medieval armor your son might enjoy seeing.

According to them, de Gaulle liberated France

Wait, what? That's not what happened 🥹?

Joke aside, in Paris there is something for many periods of history... Many great tips already, but I will add one: if he is very much into the Renaissance period, besides the paintings at the Louvre, there is a Renaissance palace with an interesting museum at Ecouen, an easy train ride away from Gare du Nord. It is beautiful (don't expect a Chenonceau or a Chambord, but it holds its weight regardless), and the museum is good. I would not typically suggest this visit to first-timers, but if this period is of interest, then it is worth the side-trip.

These are all great suggestions! Thanks so much! Thinking we will most likely stick to Paris. I'm going to look up all these museum suggestions! My son is a geo-political wiz! He loves learning about the history of how each country came to be-why they have the boundaries they do and what happened politically to make them how they are!

Thinking we will most likely stick to Paris

Good thinking!

My son is a geo-political wiz! He loves learning about the history of how each country came to be-why they have the boundaries they do and what happened politically to make them how they are!

Ah, in that case, I highly recommend the The Musée Carnavalet, which is the museum dedicated to the history of Paris. Not quite the same as country boundaries, but I suspect he'll find it fascinating nonetheless. Plus it recently reopened after a major renovation, so your timing is great.

I'd also recommend taking the Metro out to the Château de Vincennes. It gives you such a sense of the depth and breadth of French history, and makes a terrific excursion (I wouldn't even call it a day trip, more of a suburban jaunt!)

Finally, for the ultimate history aficionado experience (and I say that as the highest compliment), see if you can arrange to walk past 56 rue Jacob, on the Left Bank (Google Map pulls it right up). This is the former site of the Hotel d'York--the place where the Treaty of Paris was signed by John Adams, John Jay, and Benjamin Franklin...in other words, the literal birthplace of the United States of America. If he loves political boundaries, you can't do much better than the origin of one's own country. Be prepared: There's nothing historic there now -- in fact, there may or may not even be a plaque in French. But I think it would be pretty cool for a history lover to stand in front of the spot where the United States was officially signed into existence.

My son is a geo-political wiz! He loves learning about the history of how each country came to be-why they have the boundaries they do and what happened politically to make them how they are!

Does he like old maps? At 6 or 8 Rue Vivienne, right by the entrance to the Galerie Vivienne (close to the Palais Royal, and worth a visit!), there is a great antique map bookstore. See also Librairie Le Bail, very close to Notre Dame (but the one at the Galerie Vivienne is more casual).

Regarding this:

Be prepared: There's nothing historic there now -- in fact, there may or may not even be a plaque in French. But I think it would be pretty cool for a history lover to stand in front of the spot where the United States was officially signed into existence.

There is a plaque at 56 rue Jacob, visible on Google Street View. I had no idea about that event!

If you go to Strasbourg, tell your son not to use the expression "German-France" in front of locals, I know some who would not appreciate it at all.