I. To keep fairies away, you keep iron around—because fairies are “allergic” to iron, which is where putting a horseshoe above a door came from (because fairies can’t come through a door if it’s got iron on it).
II. Rings of mushrooms—those are fairy rings, and at night fairies come out to dance in them and you’re not supposed to walk through them, because if you do the fairies will take you away and leave a changeling in your place…
III. Changelings are like fairy babies put in the human world because fairies want human children so they leave fairy babies, or fey, in their place.
I vaguely remember a story where a girl is a changeling and nobody knows it for a really long time, but eventually they figure it out and the reason there’s a changeling, and the way they figure out she’s a changeling is because she’s allergic to iron.
How did you come across this folklore: “I probably got this through family or read these things somewhere, but I’m not sure… possibly my grandmother told me.”
Other information: “these are just some general things I’ve heard about fairies, individually, not necessarily forming a coherent story.”
These are just bits and pieces of existing folk beliefs, supposedly deriving from the Irish tradition/”fairy faith,” but handing them down, even in this fragmented form, keeps them alive and shows the resilience of folk beliefs against mainstream or popular culture, which has trivialized these beliefs into commercial and often comical representations (such as Disney’s Tinkerbell character).