There are as many versions of the origins of faeries as there are types of faerie. I have listed a few below for your information and entertainment. My personal favourite and hence the one I would like to believe is fom Sir James Barrie.
Sir James M. Barrie suggests that "When the first baby laughed for the first time, the laugh broke into a thousand pieces and they all went skipping about, and that was the beginning of faeries"
Roman Myth tells how faeries were originally immortal beings who lived in Italy, and spread through the world with the growth of the Roman Empire.
Early myths consider faeries to be the elemental nature spirits of the trees, hills, and waters. In truth this is what I really believe
Early Christian maintain that faeries are the spirits of unbaptized children, fallen angels, or ancient druids not good enough for heaven and too good for hell they are live in the middle world.
Icelandic myth tells how faeries were the unwashed children of Eve that she hid from Gods sight, God decreed that these hidden children would remain hidden forever from the sight of man and they became the elves and faerie folk.
Celtic Mythology Tells how the Tuatha De Dannan, the last generation of gods to rule Ireland, learned magic crafts and knowledge. With the coming of christianity they took up residance underground as the fairies.
What I actually believe I believe that everything natural is and contains energy. This energy can be sensed and seometimes seen by those sensitive to it's nature. It is most often seen as a shimmering out of the corner of the eye. I believe that fairie is the name given to those little shimmers of energy which have life and movement of their own.