The Breeding Pen is where all baby animals from both the Sky Zoo and the Space Zoo are bred. It is located at the cannon end of the Sky Zoo, and can only house one breeding pair at a time. To breed another baby animal, the player must either wait for the current one to finish or complete the breeding process early with . The longer the player has left to breed the animal, the more coins they have to spend. The rarer an animal is, the longer it takes to breed. The breeding pen is unlocked at Savannah 3.
More information on baby animals and how to obtain them in the first place can be seen here.