1. My little sister is very beautiful.
Mi hermanita es muy hermosa.

2. White rice
Arroz blanco

3. The little girl is six years old.
La chicita tiene seis años.

4. My grandparents are Koreans.
Mi abuelos son Coreanos.

5. I'm Japanese American.
Soy Americano japonès.

6. I'm an African American woman.
Soy un mujer Americana Africana.

They all are correct with the exception of number 3. It should be La niña chicita tiene seis años. You have to add niña ( meaning girl), because chicita just means little one. It´s implied that whoever is the little one is a female; but whether she is an small adult woman or a child is ambiguous without adding the word niña. In extreme, rare cases, It could get even be more confusing, because the adjective chicita could be use to modify feminine objects and concepts. Also saying chicita to a person (usually said to a girl or woman but some use the word to harass men by emasculating them) can be seen as cheeky to both men and women. E.g. Hola, chicita which is the equivalent to hey baby.