Paris
Notre Dame - Ile-de-la-Cite

This is the oldest part of Paris. Around 300 BC, a Celtic tribe called the Parisii plunked themselves down on the islands in the Seine. Things went on from there - the Romans used the river as a trade route, in later centuries the island was a crowded medieval city, from which Notre Dame cathedral rose to its glorious heights. During the French revolution, Marie Antoinette stuck it out in her cell in the Conciergerie prison.

Notre Dame Cathedral -
Notre Dame is the heart of Paris, and a symbol of France. Due to a devastating fire, CATHEDRAL IS CLOSED.
Slowly walk through the cathedral, soaking up the glorious stained glass windows and those airy Gothic stone arches that gracefully bridge the empty spaces and meet in the middle at the keystone. When this cathedral was built in the Middle Ages, there were no architectural drawing programs, no cranes to hoist everything up, no nail guns, no steel, and yet, Notre Dame de Paris stands as a stunning example of the lightness of stone.
Cathedral exterior - At the main entrance, in the central portal is a Last Judgement scene, on the left angel holding a scale, along with the saved, devils and people headed to hell on the right, Christ is above. The long line of statues above the cathedral are kings of Judah (all wear crowns). Tip: Bring binoculars to look at the sculptures higher up.
Cathedral interior - Inside the cathedral, don't miss the excellent model, really gives kids an idea of the structure of a Gothic cathedral with flying buttresses, and a diorama showing how it was built.
Look for a statue of Joan of Arc, carved reliefs in the center with scenes of the life of Christ, and medieval tomb of the Bishop of Paris, Simon Matifas de Bucy, with a lion at his feet.
Tower Tour - One of the best things to do in Paris with kids is to go up the South Tower to see the gargoyles on top of Notre Dame (Quasimodo territory). Climb up the tower, 422 steps, round and round, until you reach a landing, and there are the gargoyles! Some gargoyles are skinny, with shoulders hunched, hoping for their next meal, while others are chomping on grapes and chicken, and looking very well fed.
After you've goggled at the gargoyles, step into the belfry to see the Emmanuel bell, the huge 13 ton bell that's rung for great occasions. (There are 11 great bells of Notre Dame, and at various times of the day, you'll hear the bells rung.)
Continue climbing up the next steps to top of the tower, , with fabulous views of the cathedral spire, flying buttresses that keep the church from falling down, and fabulous views of Ile de la Cite and Paris in all directions.
The South Tower is something for kids of all ages (even petulant teenagers will be impressed), and it's not a guided tour per se, so children can go at their own pace. Wire netting is put up at all open-air places, no there's no worry about little kids getting too close to the edge. The steps up the tower are easy to climb (we saw lots of little kids going up), but the steps are quite narrow, and it wouldn't be easy to manage with an infant in a baby backpack. The tower is open daily.
Notre Dame play place - After you've visited the cathedral, there is a charming little play area on the south side of the church, with little bouncy things and park benches. Any exhausted parent can sit peacefully to watch the boats on the Seine, while the kids play under the shadow of this magnificent cathedral.
Sainte-Chapelle - Don't miss this luminous gem of 13th century Gothic architecture. In the Upper Chapel, sit down briefly to gaze at the ethereal blue and red stained glass windows. Go down to the Lower Chapel, originally a shrine to display holy relics. On the ceiling, gilded stars sparkle in a deep blue ceiling, supported by columns covered with golden fleur-de-lis and painted castles.
Square du Vert-Galant - At the western tip of Ile de la Cite (at the Pont de Neuf) is a small shady park with benches. Grab a sandwich and eat your lunch outdoors in the sunshine, watching boats go by on the Seine.
Go for an ice cream - Walk over to the Ile St-Louis for an ice cream at Berthillon (right next to the bridge that connects Ile de la Cite with Ile St-Louis). Delicious flavors of ice cream and sorbet - chocolate, vanilla, nougat, raspberry, strawberry, lemon, pear, orange and more. Long lines in summer, but a fun treat. Kids can sit on the embankment, munching their ice creams, with Notre Dame in the background.