The translation was "the children believe men." The possibilities were: "les enfants croient les hommes" and "les enfants croient des hommes." I chose only the one with "des hommes" because the other sentence is "the children believe the men," which is saying something different. I was told I was wrong and had no opportunity to register a complaint.
In absence of an explicit "some men", the sentence would most likely be interpreted as "all the men".
In other words, "the children believe men" means "les enfants croient les hommes", i.e. from a general standpoint.
To get the meaning "les enfants croient des hommes", you have to write explicitely "the children believe some men".
The difference between French and English about the necessity to use an explicit "some" or "all the" or not caused some famous problems: http://en.wikipedia.org/wiki/United_Nations_Security_Council_Resolution_242#French_version_vs._English_version_of_text