Ducklings are animals that are very momentary additions to wilds.io, appearing every Easter. Rest of the year they are not in the game, however are still in coding. The old ducklings (before Easter 2017) just followed the player and did nothing else (no healing).
Easter
The Easter 2017 update was released adding ducklings and eggs. The ducklings would appear when you picked up eggs, which could let you have an infinite number of ducklings. When the player was hurt, the duckling would give 1 HP to the player, and die/vanish. The update was a momentary update.
Player Traxido with ducklings
According to Rezoner's tweet, ducklings are in fact chicks or chickens:
Player and Builder Egzekutor with ducklings
A chick coming out of a egg during the Easter Event
Chicks healing the player