Many people might not consider taking their children to France's museums but even young children can appreciate the Louvre's incredible treasures in its opulent palace setting. You can pique your child's interest with the Louvre's own interactive site for children or printing out their treasure hunts for families (select parcours-jeux on their family page).
On the first Sunday of the month, many museums in France offer free admission. We'd planned to take advantage of this offer to visit the Louvre (the world's most visited museum), but instead we went the following day, thinking that it would be less crowded if most people had come the day before. Perhaps this was true, but in summer there are such hoards of tourists that any dip in attendance was imperceptible! You can try to avoid the crowds by arriving early or when the Louvre is open very late on Wednesdays or Fridays. (Kids under 18 enter free everyday.)