An Air B&B is absolutely the best option with kids.
mefoghorn said:
Sounds like Brooke knows her stuff. But here's my priorities after a few visits:
1. Musee D'Orsay (museum of impressionism in an old train station)
2. Day trip and tour of Versailles, including grounds
3. Picnic and hanging out in the park below Eiffel Tower, enjoying the views of it, people watching.
4. Plenty of time to try various crepes from stalls in the streets or cafes.
5. Window shopping up and down the Champs Elysees
6. Restoration of Notre Dame Cathedral sounds very promising.
^ This is rock-solid advice.
I am completely in agreement with the idea that everyone should visit the d'Orsay before they visit the Louvre, particularly with kids or with adults who do not have a solid command of art history. With kids, I found the d'Orsay to be a LOT more digestible than the Louvre, and I have taken my kids (then 14 and 8) to both of them. There is a really competent sit-down restaurant upstairs in the d'Orsay, with one of the clock windows inside the restaurant, such that you can get a picture of your children with the clock in the background. The other restaurant, which looks like a Baroque ballroom and is behind the indoor clock, is also good, but it's not as good.
To the idea of a picnic by the Eiffel Tower, there's an open air market called the Rue Cler. With a bag, you can assemble a picnic (in the way of French shopping), from the small shops along the road, item by item, and have a wonderful meal. Le champs de Mars is right around the corner. I have eaten 100-200 meals in Paris, and I've never done anything that delighted me more than that picnic with my kids.
Versailles is entirely worth the trip, and the gardens are better than the palace itself. There is a really very good sit-down restaurant inside of Versailles. The French are very fussy about the quality of food inside cultural monuments, and this one is a winner.
If you're looking for something to do outside of Paris, I suggest Mont St. Michel.

Specifically, I suggest spending the night on the island and letting your child wander the streets in the early morning before the tourists arrive. The drive time from Paris is about 4 hours, and you can break up the trip with Rouen or the (truly unspeakable awesomeness of) Chartres.
My general inclination is that every little kid who goes to Europe should have some sort of immersive medieval overnight experience. For my older daughter, that was Carcassonne at age 14. For my younger daughter, it was Carcassonne at 8 and Bruges at 10.
Mont St. Michel and Rothenberg occupy that space in my imagination, even though I was in my 20s before I went to Europe for the first time.
To that end, I would actually prioritize Chartres over Notre Dame de Paris. I have not taken my children to either of them, but I have been to both. I felt that the combination of a quieter environment and more careful historical preservation at Chartres made for a better experience. All of that said, I took my children to La Sainte Chapelle as their first exposure to gothic architecture.