The King drops dead, and the heir is his newborn son. Uncle Otto - with a name like that, how could they not know? - arranges to have the kid poisoned. However, she prays for her brother back, and being royalty, angels and G*d show up to grant her wish.
I'm not sure what sort of message the film makers intended to offer their audience with this short subject, but the message I got out of it is that the poor needn't bother praying, because miracles are reserved for the rich and powerful.
That's a nice crèche that the angel vanishes the baby out of to replace with the infant prince. Don't get me started about that.