I personally believe that the subtitle of this wonderful magic realist classic points towards the way in which to understand and appreciate it we must become "like children." The author has written a tale that will only frustrate and confuse us if we remain like adults, seeking meaning and definitive answers for what certain actions, characters and objects represent or mean. The subtitle, "A Tale for Children," seems to point towards the way in which we must suspend such adult concerns and just sit back and enjoy the sheer inventiveness and genius of the author.
Many critics point towards the sense of ambiguity and uncertainty created in the story. We never are told what precisely the old man with the wings "means." We are given no definitive clues towards his identity: is he an angel? A freak? Or something else? We expect stories to have meanings and to communicate some kind of message, and Marquez in this tale seems to be deliberately playing with such expectations, tantalising us with various possibilities but witholding any firm answers from us.
Note how Marquez does this, simultaneously poking fun at the villagers and their supersitions, whilst at the same time in places seeming to expect us to trust in what we know to be impossible. Consider the characters of this story: a man with wings, a woman who has changed into a spider and a man who is unable to sleep because of the noise of the stars. What are we meant to make of such phenomenons? Are we supposed to make anything of them at all? Perhaps, therefore, the subtitle is deliberately ironic, pointing towards the way in which we must suspend our desire to find clear-cut responses to such questions and just enjoy the genius of storytelling.