Halflings is a misnomer and mislabeling of anyone with even a touch of Fae magic in their DNA.
Fact of life: Far too many Fae men, before they reach their final level of maturity (usually at about 150 years, some much later than that) are, in an old term mostly used in the romance genre, RAKES. They're selfish, hedonistic, out for what makes them happy with no regard for who is hurt and how many hearts they break. Because Fae men are also charmers. And quite frankly, they utterly believe they have found their true love, and are completely faithful and loyal while they are with the poor, deluded girl. Even if their current "true love" is the tenth or the twentieth since they fled to Earth to go adventuring.
Fae fact of life related to the previous fact of life: Fae men love children, mostly because they are rather childish themselves, but also because children have a natural magic of their own. The scent of magic given off by children is irresistible. So in the selfish, childish logic of Fae men without any women nearby to slap them into some semblance of responsibility (this can include their mothers, their aunts, their grandmothers, their sisters, their wives, and their daughters), it only makes sense to make more children, and raise the magical quotient in the atmosphere. So, Fae men like to settle down and have lots of Halfling babies with their human sweethearts.
And the next Fae fact of life affects the previous one: when their human wife and sweetheart gets old and dies, the Fae man has to take off, fake his death, get out of Dodge before someone realizes, "Hey, how come he's still strong and active when his wife shriveled up and died of old age?" And yes, far too many Fae men forget to use and renew their illusion spells that make them appear to age at the same rate as their sweethearts. Or in their completely real grief, they lose control of those spells and suddenly they look like they did the day they fell in love and settled down, twenty, thirty, forty years before. So, the Fae man has to take off, leaving behind his Halfling children. Usually without telling them about their heritage.
Granted, some Fae men do make some effort to keep track of their Halfling offspring, and their offspring. The responsible ones do it themselves, or if they get trapped by Need or family responsibilities and dragged back to the Fae realms, they apply to the Ministry of Oversight of Halflings to keep track of their descendants.
Because at one time or another, those Halflings will perform some small bit of magic, involuntarily, accidentally, usually from a moment of great stress or danger or emotional upheaval. Unconscious use of magic could be dangerous, at the very least. The Halflings awakening to their magical heritage will get in enormous trouble when that happens. So they will need rescuing, as well as a Changeling Sponsor, which will be discussed later. The Ministry of Oversight of Halflings tries to identify these descendants, especially the ones with the emotional and mental capacity to adapt nicely to the Fae life, before they get into trouble. They will send their agents to test the Halfling and determine if recruiting them will be in the best interests of both that person and the Fae community in general.
Any Halfling can become a Changeling.
The term Changeling is a misnomer, in terms of the common belief that a Fae child, usually a troublemaker or unattractive in some way, either physically or in terms of stunted magic, is exchanged for a human baby. The human child is taken to the Fae realm, supposedly, and treated like a pet until he or she is no longer cute and cuddly, or starts to age, and then is dropped back into the human realm to suffer and most often end up in an asylum for the mentally deranged or even the criminally insane. What happens to the Fae child who grows up among humans and discovers his or her magical heritage, and how he or she wreaks havoc on the world around him or finds his or her way back to the Fae realm, supposedly to wreak havoc on the family who drop kicked him out of their lives is neither here nor there.
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Because it doesn't happen.
Changelings are not switched at birth. Changelings are Halflings who go through the magical gene therapy and educational process to awaken their magical heritage and insert them smoothly and pleasantly into Fae society.
Side Note: However, there is some fact and truth that supports the false belief that Fae kidnap human children.
First of all, anybody with any sense at all knows children have a magic of their own. The Fae, being essentially magical creatures, found it hard to resist the surge of energy, alertness and personal magic that came from being in the presence of just a few Human children. Which was why the false belief in Fae kidnapping infants became so prevalent and so frustratingly hard to stamp out. There were always cheats who made a grab for a quick infusion of power, usually to get themselves out of bigger trouble with someone who could see through their illusions and disguises. They made the mistake of trying to take the children with them, instead of just sitting still and waiting until their energy had been replenished. Everyone knew moving targets were easier to see. Only idiots took off and wasted some of that desperately needed magic in trying for speed or flight or even invisibility. Yes, there were some greedy sorts, usually those with an eye on overturning the social strata within the Fae Enclaves, who did gather up crowds of Human children for a steady power source. They were the exception, and they always made mistakes. Starting with forgetting to hide that beacon of power that could be seen from twenty miles away. As a rule, Fae didn’t kidnap children. Human children were too noisy and smelly and hard to corral, as a general rule.
As time went on and the Fae retreated more and more to the other dimensions, some even cutting off all traffic to and through the human realms, most Fae developed a disdain for the raw power that came from Human children. Some claimed there was a gaminess to it that was distressing. Part of that could be attributed to the Industrial Revolution, which not only polluted the physical atmosphere, but polluted the magical atmosphere by shortening childhood. As the 20th century turned into the 21st, there was less magic to be found out in the erroneously labeled "real world," the Human realms.
Another however: there are pockets of magic scattered throughout the Human realms, and quite often, investigation will reveal that a small community of Fae are living at the center of those pockets. They aren't generating that magic, but cultivating it, nurturing it, by cultivating the magic in the minds and hearts of children and enabling these children to hold onto their magic potential as they grow older--in essence helping them to avoid growing up, somewhat in the aspect of Peter Pan and the Lost Boys refusing to grow up. There is a growing tendency for Fae with the talent for children to find themselves quite happily and healthily settled into careers in education, especially childcare, where they can encourage fantasy play. The work is quite strenuous, but they receive far more nourishment for their own magic from the children under their care than they ever expend on protecting the children in their charge from the draining, debilitating effect of the modern, materialistic, skeptical, non-magical, falsely labeled "realistic" world. Sadly, for all the joy the children find in their magical play, creating magical spells, thinning the curtain between the real world and the Fae realms so they actually do glimpse magical creatures on the edges of their playgrounds, far too many do grow up and "lose" their magic. They make choices and walk away from their pure childhood belief, and shut down the stream of magic potential inside themselves. Because of that, even the best of the Fae childcare workers eventually give up the careers that give them so much fulfillment, and retreat back to the Fae realms, so they don't have to see their beloved children grow up, grow out of their belief and their magic, and grow gray and dry, and essentially die in their spirits long before their bodies do so.
