Chica is the feminine of
Chico "small, little", used as a substantive it means "little one", and is often used to refer to a child. Chiquita/Chiquito is a diminutive, a broad term that refers to noun forms (in this case formed with the -ita suffix) that have a range of meanings depending on context that can include belittling, diminution of force, or simply endearment.