The Children's Farm is a farm-themed extension to your zoo. Unlike other regions, you don't need the Zoological Society to unlock it (although if you do have it, you will be able to access it through there).
All players level 6 and up can access the Children's Farm by clicking on the premium account menu in the top left corner and using the "To Farm" button:
The Children's Farm starts out with a bunch of obstacles, that can be cleared.
There's a whole array of farm-themed decorations for the Children's Farm and the enclosures within it. These will also give you Premium Coins, which increase your premium account level.
There are exclusive animals that can only be kept on your farm: Holstein Cattle, Valais Blacknecks, Mangalitsa Pigs, & Leghorn Chickens. These can be obtained from Diamond Boosters, which you can only get with a level 10 or higher premium account.
Many regular zoo animals can also be kept on your farm: Water Buffalo, Wild Turkey, Yak, East Friesian Sheep, Shetland Pony, Domestic Donkey, Llama, Reindeer, Alpaca, Pot-Bellied Pig, Mallard, Domestic Horse, Sheep, Domestic Pig, Goat, Peacock.