We are just back, took 7yr old ds. Stayed in St Germain, as great to walk to so many places, stayed in Hotel Regent, rue Dauphine, just near Pont Neuf, so easy to get to from Odeon metro, if you are coming in from Gare du Nord, or easy for the RER train direct from Charles de Gaulle airport.
First afternoon we walked to Pompidou and Notre Dame. Lots of restaurants and shops near the hotel.
2nd day, we walked to Louvre (10mins) to see Mona Lisa, which ds was disappointed with, as she was so small! He loved the amazing ceilings in the museum. From there we caught the no95 bus up to Monmartre to the Sacre Couer. (lots of buses go from Louvre so a good place to be near to). Climbed up the spiral stone staircase to get right up to the top, which ds loved. Fantastice views!
3rd day, was the Eiffel Tower, I think everyone in France was there, it took 90mins to queue, and we arrived at 10.15am. I would suggest skipping breakfast, getting there when it opens at 9am, and having breakfast afterwards, or get a crossaint/pain au chocolat in the cafe on stage 1. Despite the queue, ds loved it, it is so HUGE and awesome, we went to level, 2, not the very very top.
Onto a batobus back to St Germain. Batobus don't do commentary, the bigger ones do the full tour and full commentary. Batobus you can get 1 day/2 day tickets, and it does a loop of about 8 stops of the main sights. It's really good.
Can recommend Printemps store in the centre, amazing cafe on the 9th floor, again with great views. Toy department was appreciated by ds after so much culture!
The PAUL chain of boulangerie/cafes are really good for breakfasts, and amazing types of bread and pastries, they seemed to be in all the main places.