How do I get the Hatchlings and where can I view my collection?

To find Hatchlings, you simply play the levels in the game. You can see on which levels you can find the Hatchlings on top of the main screen and in the Collection menu.

You can open the Collection menu by clicking on the shirt-button at the bottom left corner of the main screen. In the Collection menu you can view all the unlocked Hatchlings and their outfits.