You have four days in Paris - what do you do?

You could spend double that in Paris and not do the things you want to do. A baby does complicate it. Why Spain and Paris?

If he's really really into WW2 you could add Normandy, its just not a lot of time in Paris.

The things you MUST do imo:

Louvre
D'Orsay
Eiffel Tower/Trocadero
Montmarte/Sacre Couer
Notre Dame (outside, since it is closed)
Walk along Seine/Seine river cruise
Arc de Triumphe
Pantheon

Things that are pretty cool as well to try and do:

Champs-Elysee (personally I couldn't care less about this)
Catacombs
Sit at famous cafe
Walk through Le Marais neighborhood and Place de Voges
Bastille
Tuileries Gardens
Rodin Museum
Centre Pompidou


If you do Normandy, definitely don't do Versailles.

With Notre Dame closed, you might want to go to Chartres, to see the incredible cathedral that UNESCO calls "the high point of French Gothic art."

It's a little over an hour outside of Paris.

You have so many options if everything is open. Our late September itinerary--

Day 1 - Check into hotel in 2nd Arr., walk to Montmartre for Secret Food Tour, walk around Montmartre, walk back to Arc De Triomphe area

Day 2 - Rooftop bar at swanky hotel for brunch, walk to Eiffel Tower and relax on lawn with wine/cheese, walk along Seine to see Musee D'Orsay

Day 3 - Shopping in 2nd Arr., see the Louvre, walk by Notre Dame, and nighttime walk around Marais

Day 4 - Train to Versailles for full-day visit (incl. Grand Trianon, Petit Trianon, and the Hameau) and see some of nearby city of Versailles

One thing I forgot to mention:

EAT.

Paris is one of the best food cities on earth. It is truly incredible.

As an add on to the many great suggestions, I would add taking a stroll through Pere Lachaise (sp) cemetery. Many many famous Parisians buried there as well as Jim Morrison.

I'm a history buff and that was a very cool couple of hours there and its also away from much of the crowds. Think of it as an outdoor Westminster Abbey (Poets Corner, etc.)

We love to visit Notre Dame but haven’t been since the fire. Sacre’ Coeur is also amazing. The views of the city alone are worth a visit. Saint Germain has some great food. I remember the Gregorie but there a so many. Museums are also worth visiting, we loved Musee d’Orsay. Also fun to just walk and find something unexpected.

Lots of great day trips using railroads. We visited Reims in Champagne region.

This is what I did in Paris in 4 days:
-Walked the Latin Quarter: had a coffee at a famous cafe.
-Saw Notre Dame
-Night coach tour; dinner at a small cafe with unlimited “table wine”
-walked to the Eiffel Tower at night to see it light up, followed by drinking wine at a nearby sidewalk cafe with newly found friends
-Seine River Cruise with a massive hangover
-The Louvre
-Rode the Metro many times
-Had lunch at a small cafe with a carafe of wine
-Saw most of the major sights: Arc d’Triomphe, Place de La Concorde, Pompidou Centre, (too many to name).
-Visited Place d’Italie looking for Mr. et Mme. Thibaut from my high school French lessons(couldn’t find them).
-Catacombs
-Sat in an Aussie bar for two hours drinking proper beer.
-Visited a Fromagerie and bought some great cheese and wine.
-Versailles
-Went to the top of Eiffel Tower at night
-Ate at a mostly local restaurant. Great food and bottle of wine. Never thought I’d like a carrot soup with fish in it.
-Musee d’Orsay (which was the highlight of my visit to Paris).

I’m sure I’m missing a couple things. But I think I got in a lot of things for four days.