That's not a common wording for most native speakers of today's English, I believe, so while it corresponds more closely to the German wording, I wouldn't consider it "neater" as it is less natural for many speakers.
Even closer would be "How many children hast thou?", but that would be natural for an even smaller number of today's native speakers, I believe.
Thanks for the "vote of confidence" for "How many children have you?" being common in at least some places! It's difficult to be aware of English usage in all places in the world.
My impression is still that worldwide (and especially in the US, given that Duolingo generally uses US English), it's less common, so I still think that it's not "the neatest translation". But it's accepted now.