You will need to find the missing Animals in the "Summer Camp"/ "Adventure" Area for the carrousel.
Those being: 3 Horses and one Pig.
1. Horse Number 1 is right next to the Carousel behind the 2 Vending Machines
2. The Pig is on the wooden Watchtower when you go right from the 2 Vending machines, behind the Camping Table with the 2 crocodiles. (a ladder is on the back)
3. If you continue that trail you will get to the beach and on that beach is a crashed rollercoaster cart, next to it is another horse.
4. if you follow that rollercoaster into the Mine and through the Vault door, you will find the last Horse stuck between the carts in this room
This will give you the Achievement