While "pato" generally refers to a duck, it can also be used specifically for a duckling, depending on the context.
Here are some examples:
* Isang maliit na pato - A small duckling
* Ang mga pato ay naglalaro sa ilog - The ducklings are playing in the river.
You can also use "batang pato" which literally translates to "child duck" to emphasize that you are referring to a young duck.