Like most words, there can be many definitions or equivalents in another language. I think Duolingo just limits each mouse-over to show 3 of them. That's why you might not see all the possible equivalents. That doesn't mean they're all appropriate for the sentence, because sometimes what a words means may differ when accompanying other words. In this sentence, since "barn" is following "sina" (which is plural), the meaning of "barn" must be plural. It should take both "children" and "kids", but not "child" or "kid".