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.)
Entering the Louvre from the east (La Cour Carrée) gives a beautiful view of the courtyard. From there we walked towards I.M. Pei's glass Pyramid and we laughed to see so many tourists taking the same photo: balancing on a pedestal and pretending to hold the pyramid on their hand or dangling it from their fingers. There were so many tourists! (It appeared that many of them brought along their selfie sticks--probably purchased from hawkers at the Eiffel Tower!).
The line to enter through the Pyramid is long--wise tourists know to buy their tickets online, pick them up in a store like FNAC, and enter through a lesser known entrance like the one on the Rue de Rivoli. Otherwise, tickets can be bought inside. We were grateful to skip the line to enter when an employee spotted our baby and let us enter via a separate door. You will find this is common in Paris--pregnant women, mothers with a baby, and handicapped people are often given priority entry and seating, whether on the Metro or in a café. It's a delight for mothers!
Ticket lines inside are also long, but if you have a chip-and-pin credit card, you can use the self-service ticket machines. (Many American banks are switching to chip-and-pin credit cards this year, so you may soon be able to use more payment machines in Europe.) You can also borrow a baby carrier or stroller free from the info desk in exchange for an I.D. card. (A stroller is nice to have but there are many areas only accessible by stairs.)
There are three wings inside; the Sully wing is of the most interest to children and perhaps adults as well, so consider starting there. There you'll see the enormous base and walls of the castle-like medieval Louvre, followed by the sphinxes, treasures, and sarcophagi of ancient Egypt. Follow the children's treasure hunt printout from on the Louvre's website to keep children interested, then quickly make your way towards the Winged Victory of Samothrace and the Mona Lisa when your children are fading. (If you spent one minute in front of each of the Louvre's items without taking time to sleep, you would be there nearly one month! Most children can only handle about 45 minutes there.)
When you've had enough of the Louvre's incredible opulence, head outside to the Jardin des Tuileries. There you can refresh with snacks, a picnic, or ice cream from the vendors. On the right you'll find a fountain where children can rent a large sailboat and a stick to keep it moving (currently 2€ for 20 minutes). In summer a carnival takes over the northern side of the gardens, but unless you have older children, I suggest heading towards the merry-go-round, trampolines, and excellent playground with covered seating for parents. You'll find a good photo opportunity at the bust of Charles Perrault (celebrated French author of fables such as Puss in Boots and Sleeping Beauty), where your child can join hands with the statues of children playing around him.
You can leave the gardens via the western entrance near the Place de la Concorde, where you will find toilets and, to the right, a Metro station. (the Obelisque at Place de la Concorde is the oldest monument in Paris--a gift from Egypt. The site is also where many lost their lives via guillotine.) From this end of the park, you'll have a decent view of the Champs Élysées and the distant Arc de Triomphe.
Have you visited the Louvre? What did you most appreciate seeing there?