For a bit of adventure, animals, and adrenaline Six Flags is the place to go in Mexico City. Unlike other amusement parks, they feature a range of activities—many of which you won't find in the US—that cater to all ages. Explore the themed villages, swim with dolphins, or ride the roller coasters. I suggest you checkout Pueblo Mexicano, Pueblo Francés, Pueblo Polinesio, Pueblo Vaquero, and the Bugs Bunny Pueblo.
If you buy your tickets online you can get them for half price as opposed to the $40 gate price. Buy a VIP pass if you don't relish waiting in long lines and go early to avoid the heat and the crowds. As the only Six Flags in Latin America, this amusement park is definitely worth the trip.