When Hatchlings are unlocked, you can choose an outfit for them. You can purchase more outfits with coins and yarn or by obtaining them from mystery chests.

You can view the outfit options for your Hatchlings by selecting a Hatchling in the Collection menu. Available outfits for the Hatchling will be displayed at the bottom. You will see both owned outfits and those available for purchase. Outfits you currently may not have will display their coin and yarn prices.