Hi pella, you will actually see a difference when they will be adult.
For every species you will see a 1/4, a 2/4, a 3/4, a 4/4. Those actually represents different stage of the creatures that you can obtain when they are fully grown. The 1/4 and the 2/4 represents the parents, and the 3/4 and the 4/4 represents the child.
For exemple :
1/4 ==»
2/4 ==»
3/4 ==»
4/4 ==»
Hope it clarifies a bit more.
If you have anymore questions, feel free to ask !
Efellia