"Les enfants sont des hommes."
This interpretation is a bit far fetched, I think, because in French we would not say it that way because it would be too vague. We might say "les enfants proviennent des hommes" which would be grammatically correct but the statement in itself would be a little stupid in my opinion.
les enfants sont des hommes. I translated as 'the children are the men's'. But the correct translation was the 'the children are men'. How can the children be men? Or is the sentence saying the children are males?
when first learning 'des', the definition said "some, of the, a few". Is 'of the' not possessive? Explain please. Thank you.
After reading all of the comments left previously, I still am left wondering how a native French speaker would use this phrase, if at all. Per the translation given I would have to assume that they would use it as Willis Tyne has already suggested, but that seems like a corner case. If they would use it where an English speaker would say "The children are boys" wouldn't we as learners be better served with that translation? The point of learning a language is not to do litteral word to word translation (Google translate can do that just fine) but to actually learn how to speak in a language, idioms and all.
No, it does not make sense neither in French nor in English (nor in any other language, I would think). There have been a lot of complaints about that one (and a number of others) but it seems that Duolingo has not heard them... I can propose another one to you, using the same structure : "roses are flowers" = "les roses sont des fleurs".
"sont" is the 3rd person plural form of verb "être". There is no such thing as masculine and feminine in that verbal form. For your information, conjugation of verb "être": je suis, tu es, il/elle/on est, nous sommes, vous êtes (polite and plural), ils/elles sont.
Now, "son" is a possessive adjective which has to agree with the object possessed (not with the owner): "son bateau" (his or her boat); "sa maison" (his or her house).