The Army Museum is worth a visit - it is interesting to see a less Anglo centric view of the wars, particularly WW1. The paintings are deeply grim - not ideal if you have young kids.
https://en.m.wikipedia.org/wiki/Musée_de_l%27Armée
Probably a candidate for best museum in the world, the Louvre is a great way to completely waste a day with massive crowds, sore feet, food and water shortages, closed exhibits, intense heat and even more crowds. Get a map ahead of time and check that the things you want to see aren’t closed before you go.
If you want to see an outstanding collection of art without having to face the Louvre crowds, try the Musée d'Orsay: a vastly more pleasant experience, IMO. https://en.wikipedia.org/wiki/Musée_d%27Orsay