Bois de Boulogne

http://goparis.about.com/od/parisforkids/a/Jardin-D-Acclimation-Park-In-Paris.htm
A truly paradisical "garden" for kids, the Jardin d'Acclimation was Paris' very first amusement park, opened by Napoleon III in 1860 at the sprawling Bois de Boulogne. The nearly 50-acre park was originally intended to replicate an English-style garden, but with a more scientific lean. In its modern-day incarnation, the park is both a big draw card for children and a comfortable trip down memory lane for parents, offering a gaggle of attractions, antique games, animal farm, and a children's museum, but also plenty of lush greenery and unique lounging areas to balance your energy.
Metro: Les Sablons (Line 1)
October-March daily from 10am to 6pm.
 http://www.jardindacclimatation.fr/practicalguide.pdf  
 pilet 3 eur, alla 3 a tasuta
http://www.davidlebovitz.com/2009/04/ten-great-things-to-do-with-kids/ 
This childrens’ park was actually designed in the 19th century, and although it’s been updated with lots of cool rides and play equipment there’s still an air of old Paris about the place. (The jungle boat ride with it’s period depiction of natives sitting in the grass and pith-helmet wearing colonialists is particularly, er, historic.) We love it because most of the play equipment is designed for the park itself (instead of purchased off the shelf and plopped there), which makes it far more intriguing and novel. One should definitely arrive on the “petit train” that leaves from the Porte Maillot, a narrow gauge choo-choo that chugs through the perimeter of the Bois de Boulonge before depositing you at the entrance. This place has it all: a zoo, a sprinkler park, huge expanses of park equipment for every age, and a boardwalk-like section of rides and junk food.