My answer "Their children are having breakfast" was considered wrong. I think allowed translations are just too literal. I suppose Duolingo expected "Their children are eating breakfast", as in my answer "having" was marked as mistake.
Yes indeed. I have reported the sentence of course. But, as I am not a native English speaker, I added my comment to double-check I was not wrong. I have already learned a couple of things (in English) thanks to community comments. Two birds with one stone! :-)
When ילדים is used, it can be interpreted as either "boys", "children of differing genders", or "children of unknown or unspecified gender". It's true that the grammatical gender of the word is male, but bare in mind that it there is no neuter in Hebrew and many times male is used for neuter or mixed. If I wanted to translate "their boys" I would go for הבנים שלהן.
Then we do not know how to say boys and we should avoid it in all translations. Except there are other sentences that require us to translate it with "boys". When the course contains sentences like "They are sad and they are sad", which only makes sense in a context where I am physically pointing at the groups of men and women, it is unreasonable to say that there is not enough context to allow for a translation of "boys" in this sentence.
You assume it's the same children for all mothers referred to, but it's not חד משמעית. It could talk about a group of mothers, and the children of each mother separately - and then it could well be single mothers or mothers from traditional father-mother families.
It doesn't even have to be mothers. The sentence could refer to teachers, or persons-in-charge-of-groups (what's the word?) in a summer camp...