Grammatical Cases (Nominative, Accusative, Dative, Genitive)
When do I add an -n to plural nouns in the dative case?
In the dative plural, if the plural noun does not already end in -s or -n, you add an -n to the end of the noun.
Example
die Kinder (Nom. Plural) → den Kindern (Dat. Plural)
die Frauen (Nom. Plural) → den Frauen (Dat. Plural - already ends in -n)
die Autos (Nom. Plural) → den Autos (Dat. Plural - already ends in -s)