Try and do a search, as I’ve posted several times with info on similar threads.
Jardin d’Acclimatation is great; my 13 yo still loves it. Top tip: visit the Fondation Louis Vuitton next door (current expo is David Hockney); it then gives you free entry into the gardens. A good way to combine a bit of culture.
Second Atelier des Lumieres.
The Musée de la Prefecture du Police is free and very interesting for both adults and kids alike. Lots of exhibits ranging from ancient to modern, like drones and machine guns. Just need to book a slot. It’s inside the actual police station, which is quite cool. It’s only in French, obvs.
Other free museums: Carnevalet in the Marais. Basically the museum of the city of Paris. Maison Victor Hugo on Place de Vosges: small, compact, nice art. Archives Nationale in the Marais.
Catacombs is good.
Tour Montparnasse is much cheaper than Eiffel, easier to book, and gives just a good views.
Best museums for kids imho: Citeco .. Museum of Economy. Don’t be fooled by dry subject. Starts off with tour of original Banque de France gothic building. Finishes with totally interactive exhibits that are really fun to do. We all enjoyed. Musée de la Chasse et Nature in the Marais is absolutely fascinating. Think taxidermists dream.
If you have to do the Louvre, be warned queuing times even with a timed slot are mad. Allow extra half an hour. Personally, I’d skip the Sully wing (Mona Lisa, Venus de Milo etc) and visit the Richelieu wing. Current expo is Louvre Couture, and the haute couture dresses are stunning.
Petit Palais is free, full of nice art and sculptures, has decent cafe with a lunch formule and courtyard garden, and good loos. Great pit stop half way down Champs Elysées.
Ladurée on the cheap on the Champs E…. Order your takeaway coffee, macaron etc. Sit and eat/drink on the provided seats. Cheaper than going into the restaurant.
Favourite boat trip is the Vedettes de Pont Neuf. Combine with Notre Dame; it’s absolutely stunning. Book advance (free) slot via the app, 3 days ahead, as the non ticket queue is mad.
Restaurants: any of the Bouillon chain for cheap eats. Bouilon Pigalle can be booked (essential to avoid the queue) and is v handy for Montmartre (take the back route up: Mur d’Amour/Bateau Lavoire/Moulin/buste de Dalida/Maison Rose etc).
Bouillon Julien is a stunning Art Nouveau restaurant and can be booked.
Chartier is a classic bouillon; can’t be booked but is fun to queue for the experience.
The covered passageways are beautiful. Passage Jouffroy and Verdun for shops; then Passage Panorama just opposite for restaurants and cafes.