Paris is a family friendly city and offers a lot to keep the little guys busy and entertained. The best area to stay in Paris with children would be the 6th district near the Luxembourg garden. The 7th district near the Invalides garden would also be a smart choice.
Parks in Paris are going to be your number one source of kids fun. Most paid activities will be a lot cheaper than the higher end amusement parks like Disney Paris. My park of choice for kids would be the Luxembourg Garden. You’ll find ponds to sail toy boats (for rent), outdoor puppet shows, temporary small amusement parks and pony rides. Several cafés around to refresh and playgrounds with slides and swings.
Jardin des plantes in the 5th district near Latin quarter is also a great source of entertainment for children, lots of playgrounds and a fantastic way to make their day would be the visit of the natural science museum with the dinosaur exhibit located in this park. The great Gallery of evolution also located there displays a giant whale skeleton and dead bug and reptile collections (under glass) and many other mind blowing exhibit.
La villette park in the 19th district is little more out of the way but worth your time, Lots of space to run and play. You might also want to consider near the park the largest science museum in Europe with an area dedicated to children call La cité des Enfants. they can play and learn at the same time.
River cruise, small train ride and balloon ride:
Other cool activities in Paris for kids are unusual transportation like River cruises on the Seine river with Batobus, Montmartre small train tour, or a balloon ride above the André Citroen park in the 16th district.
Paris zoos and aquariums:
Paris aquarium Cineaqua is located in the trocadero garden facing the Eiffel tower. A great moment for kids and teenagers, 10 000 fishes to watch among which 25 sharks.
Another great moment for kids with animals in Paris will be the visit of the Vincennes wood zoo recently renovated. It is located in the 12th district.
Water fun and swimming:
if your kids love water, Paris has a water park call Aquaboulevard with wave swimming pools and water slides the largest in Europe open all year. Swimming pools also are a great options. There are over 40 across the city but my favourite is the Joséphine Baker floating pool located on a giant barge along the Seine river open all year.