Formal:
* Niña pequeña: This is the most literal translation and is quite formal.
* Bebé niña: This is another formal option, emphasizing the baby aspect.
Informal:
* Bebé: This is the most common and casual way to refer to a baby girl.
* Chica pequeña: This is a more informal option, meaning "little girl."
* Niña: This is simply "girl" and can be used in most casual contexts.
Other options:
* Mi niña: "My little girl," used affectionately.
* Princesa: "Princess," used as a term of endearment.
The best option for you will depend on the specific situation and your level of comfort with the Spanish language.