The Danish word "leger" has elsewhere been translated as "play". So does the sentence refer to children playing at being parents, or to childless adults pretending, for some reason, that they have children? I know this has been mentioned before but I can't see any definitive answer.
I put as an answer 'they are pretend parents' which works in English (I appreciate it might not work in other languages!). It was marked as wrong, which I accept, but could it be a valid alternative answer?
Having come back to it again, I think there's a verb missing. It would make more sense (in English): "They are playing AT BEING parents". If of course that's what the translation would be.