In magical realism, the genre of "A Very Old Man with Enormous Wings," it's hard to tell exactly why anything is what it is, which is one of the drifining features of magical realism. There are clues to why the story carries the subtitle A Tale for Children.
First of all, the story is about an angel which is a favorite topic for children to think and hear about. Secondly, while people are coming from far and wide to dee the captive old man with wings, a circuses and carnivals also come to town. A circus or carnival is always of interest to children and provides an element of a children's tale.
There is a moral taught within the narrative, taught by the spider-woman who disobeyed her parents and was turned into a tarantula spider. She now teaches the importance of obeying one's parents.
Finally the old man with wings grows new feathers and learns anew how to fly. Flight and new beginnings are another favorite topic that children like to hear about in stories and seems to be the theme of Gabriel Jose Garcia Marquez's story: spiritual flight and new beginnings.