"Young elephants' food"
I thought one had to use 'de' if the modifier of the noun was in front of the noun. Now it wants 'des'?
This means "the food of the young elephants" with the possessive form which does not exist in French.
All possessive constructions are identical in French: owned thing + de + definite article + owner.
"Des" here is not the plural of "un/une", but the contraction of de-les
Look at the singular forms: - la nourriture du jeune éléphant (= de-le) - la nourriture de la jeune éléphante