"The children eat bananas."
Translation:Les enfants mangent des bananes.
Because "des" means some and "le" means the. So "des" is used when you are referring to any fruit in the world and "les" means you are referring to specific fruits
When you have a plural noun preceded by an adjective the partitive article des becomes de. If there is no adjective use des. This rule only applies to the partitive article des, not when des is a contraction of de + les meaning "of the" etc.