That seems to be a real problem. When I wrote my penpal from California that in Russia children are given presents by Father Frost and his granddaughter, she asked me a logical question, "And who's his wife?". Then I wrote her that it's a secret for everybody but his daughter is Spring. So, the next question arises, "And who's her husband?"
Moreover, why do Father Frost and his granddaughter come from different towns? He is from Velikiy Ustug. And she's from Kostroma (if I'm not mistaken). So, why??!!!