There's a small square very near Pompideau Center with modern sculpture that I find much more interesting than the exhibits in Pompideau Center. The building itself was interesting when it opened, although I liked the views from the escalators almost more than the building, which now doesn't seem especially cool or anything.

Some kids might be interested in some of the idiosyncratic specialized museums in Paris. There's one for clocks and, in Ecole des Mines next to Luxembourg Gardens, a museum (very limited hours) for gems. I don't think it would interest most kids, but I love to go to the House of Baccarat (crystal museum) to see the antique chandeliers, etc.