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What time of year and what are you interested in ?
If your kids are into Disney would can do 2 days in the parks (Annie Oakley show with dinner is fun too)
museums (Louvre, Musee d’Orsay, Picasso, Pompidou centre- not my favourite but popular)
walk around (and take a walking tour) you always see more of a city on foot (watch for pickpockets much worse than London)
Notre Damn, Ile de la citie
Tower (walk up to first level)
Arc Triomphe go to top for view
Place Concorde, Grand Palais and Pont Alenxandre III
Invalides
cemetry Pere Lachaise (Jim Morrison, Edith Piaf, Oscar Wilde, etc etc – best with a tour)
Boat trip on Seine perhaps with lunch or dinner
download la forchette app and save lots on restaurant bookings – do some research and book a couple of places in advance
Versailles, Chantilly (esp if you like horses, very nice chateau)