Our family of five (aged 8, 12, and 15) were very happy in the apartment, which is close to everywhere we wanted to go but Montmartre (and that was an easy bus from Quai de Louvre stop). We came to Paris to go to the museums, and it is walking distance to all of them! Because of its proximity to so many restaurants, we were able to go out relatively late at night and walk home safely.
The actual apartment is "epic," as my kids said. For those used to suburban homes, it's a bit strange, which we found delightful. There are two metal spiral staircases, one going to a loft, and the other going down to the basement shower, which looks like a "magical cave." The main floor has high-end Italian Clei murphy beds, which the kids loved.
Just to point out (and it's in the description), there are no doors, either to the loft or to the shower downstairs, but of course they're on different floors so there's privacy. I was fine with this but the pre/teen girls refused to let us walk into the kitchen when they were in the shower. Also, there's no door to close for the parents upstairs, just saying. But I would still choose this apartment again, the next time we go, it's amazing.
Jean François, merci infiniment pour de meilleur anniversaire de ma vie et une expérience magique pour ma filles!