Black Eyed Kids (AKA BEKs or Black Eyed People) are an urban legend/creepypasta story staple.
They are exactly what they sound like; people-- most often children-- with pure black eyes lacking sclera and irises. Sometimes they're also described as having sickly pale or corpse-like gray/blue-tinged skin, but not always.
Though creepy kids and black eyes have been horror story elements for ages, the oldest BEK story I could find is by a Mr. Brian Bethel, written back in 1998, supposedly based off an actual encounter. Since then, a more and more stories featuring BEKs have been cropping up, though they haven't become the wild horror phenomenon that, say, Slender man has.
Despite the name, it's not enough for the creature in question to just be a creepy kid with black eyes. BEK stories tend to hit a few specific beats:
1. One or more kids (usually two) approach someone who is inside a car or house, usually at night.
2. The person they approach feels dread and fear without comprehending why.
3. The kids will ask for entrance into a car or house (usually claiming to need aid), but their demeanor is a confident one, and they speak with the voices or articulation of adults.
4. The person approached will find usually themselves compelled to do as the kid says, and either they stop themselves, notice the kids' black eyes, and run away, or they notice the eyes, are unable to stop themselves, and presumably die horribly off screen after the kids enter their house or car. If the person was already inside somewhere when the kids showed up, the kids will mewl outside for a while before eventually vanishing.
Usually the story goes that people don't notice that there's anything physically unusual about the kids until midway through the encounter. They'll look away and look back and notice the black eyes or unusually corpse-like skin. Most stories aren't clear what exactly happens to people who allow them entrance, but it can't be good.
A few variations I've heard have include the testimonial of a man who'd been out camping and was trapped in his tent while two BEKs waited outside, begging for entry until dawn, a woman recalling when she was a small child and opened the door to two BEKs who then left of their own accord, and a whole lot of stories about people who'd turned the kids away, only to look out the windows and see them standing outside all night long.
There are also supposed to be versions with adults, but normally the adults just stand around in people's peripheral vision, looking creepy and sad and vanishing when looked straight-on. At this point, adult black-eyed creatures might as well be considered a different kind of creature from the BEK as their behavior is so different.
BEKs are sometimes considered a subclass of vampire due to the skin and insistence on permission before entering homes and cars, but how strict that's played varies story to story. Part of the creepiness that comes from BEK stories is the lack of resolution as to what, exactly, these kids are and where they come from.
Also, some people believe they're real. But people believe aliens, ghosts, and the jersey devil are real. So there you go.