"The young children eat the chocolate."
Translation:Les jeunes enfants mangent le chocolat.
It is one of those cases when the adjectives is placed in front of the noun:http://french.about.com/od/grammar/a/adjectives_4.htm
... eat the chocolate =... mangent le chocolat = specific chocolate, so definite article in both languages
... eat (some) chocolate = .... mangent du chocolat = partitive article "du "(contraction of de+le, feminine: de la) to express that they are eating "an undefined quantity of a non-countable thing".