There are quite a lot of stories about fairy godparents in the world.
Whether any of these other stories are accurate or not is unknown; when it comes to Adam Young, though, it most certainly is.
Not that his parents knew, of course. No, to them, Mr. Fell was just their kind neighbor, who ran a bookshop and was so gentle, and such a comfort to Deirdre during her pregnancy, and it had only seemed natural to give him the honor of being Adam's godfather. They had no way of knowing that he was an actual fairy, and that they could not have chosen a better guardian for their son than him.
Aziraphale- for that was his name, or at least the name we must call him- adored Adam. He was a sweet, curly-haired child, rambunctious and excitable, but not exactly ill-behaved. He was prone to naughtiness, but Aziraphale, despite professing great value in morality, had always found naughtiness rather charming. And he was careful to teach the boy- and he had many opportunities, because Adam spent a great deal of time in Aziraphale's company- to draw the line between naughtiness and truly being Bad.
When Adam was two, his parents went away for the weekend- the first time since Adam's birth that they had felt able to leave him for more than a few hours- and left Adam with his godfather, who was quite looking forward to a weekend of doting on his rascally godson, taking him out for scrumptious desserts and then reading to him from a big storybook while Adam played in the garden.
And that is where our story begins- with Adam slightly sticky and running off a large amount of sugar in the garden while Aziraphale, his fairy godfather, reads to him stories that are not quite true, but could very easily be, and a pair of golden eyes peering at them both through a crack in the garden wall that was not there earlier and will not be there later on.
Every fairy story needs a villain, right?
Crowley was a goblin king. Not THE goblin king, just the king of this particular city, and he liked to think he was very good at it. He was a tricky sort of fellow, slinking out into the mortal world to cause mischief for the humans, sometimes granting their heart’s desire in twisted ways, sometimes hiding things that they wouldn’t notice missing immediately, sometimes being helpful in ways that were sure to come back and bite them later.
He liked messing about in their gardens. Crowley loved gardens, but he loved gardens that were allowed to grow naturally, and the gardens of humans were far too neat and tidy and controlled than the wild gardens of his realm. Plants should be guided, not led, and their growth was far more luscious when they were allowed to expand in the ways that came naturally. 
And stealing children, of course. That was his favorite game, stealing children away and leading their caretakers on a merry game through his labyrinth to get them back.
They always won his game, of course. Humans were too clever, and children far too sticky, for any other outcome to emerge.
Besides, they never seemed to fall in love with him, which he tended to think was incredibly unfair. He was a very pretty goblin, at least by human standards,  and he wore very tight trousers and had nice hair, so at least one human ought to have fallen in love with him by now.
He had been watching the house for a few days now, ever since deciding that this “Tadfield” was a much better place to put his realm than the growing city he’d been keeping it in before. Cities were too big for goblin mischief; it was being thirsty and being handed a lake. There was too much , no, little villages were best, and Tadfield was so small and idyllic that it practically cried out for a goblin city. Children in a village had a right to grow up with their good neighbors lurking around to wreak havoc.
This child he liked the look of, with his soft, pretty curls, and the excited way his eyes lit up as he explored the world around him. He clearly had a streak of mischief but he was so gentle as well. The first day Crowley saw him he’d been lying perfectly still in the grass, watching a bird hopping around a few feet away, not even daring to move lest he frighten her from her meal. Crowley liked that; he approved of mischief, but he had a soft spot for true gentleness.
And now the boy was in the care of some other human than his parents, a pretty sort of human in outdated clothes  reading fairy tales to him from under the tree. It was a perfect set up: the fairy tale book would make an ironic touch that pleased Crowley’s inner dramatic, and this human was almost hypnotically pretty and very much Crowley’s type, insofar as Crowley could be said to have a “type”, which would make it all the more satisfying to make him fall in love with the goblin king.
Crowley grinned to himself, and let his form shrink down until he was a in the shape of a harmless garden snake, and slithered through the crack in the garden wall toward the spot where the boy was playing.
 Guided with a healthy dose of fear, that is.
 By goblin standards he was too tall, too thin, and too altogether human to actually be considered attractive.
 Crowley worked very hard to keep up with changing human fashion, and resented any human who couldn’t be bothered.