Pack of animals that grow with water.
This pack of animals are made from a super absorbent polymer, which grow up to 10 times their size when placed in water. It takes 3 days for them to grow. Once they have grown and absorbed the water, if left without water they return to their original size and can be used again.
These animals should be left in water for 3 days until they reach their maximum size. In this picture you can see it
In this video from the children's experiments channel you can see the practice of growing animals with children.