In my book The Fairy Realm I tried to show that the existence of fairies was a possibility. I suggested they came from another universe or dimension. The small horses reported in their company would possibly have a similar origin.
Lady Gregory, the Irish folklorist, writing in 1920, knew of at least two direct reports of such horses. A man from County Clare told her he had seen a field full of mounted fairies, whom he compared with jockeys. Another informant, J. McCreevy, claimed to have seen "red men" riding through the country, but he does not specify if these were diminutive.
In 1920 Sir Arthur Conan Doyle received a letter from Mrs Hardy of New Zealand who said she had once seen a group of eight or ten little people riding on tiny ponies.
Nearer our own time, Herbie Brennan, a well-known author, and a friend saw tiny horses. They were in County Kildare at Longstone Rath. None exceeded the size of a cocker spaniel. There were about 25 in number. This occurred in 1971.
Two tiny horses, no taller than 18", were reported from the Philippines in the 1970s.
What are we to make of all this? Are there diminutive steeds that come and go into our universe? At this juncture, no one can be certain. The existence of the horses may not be proven, but mounting evidence indicates we should not dismiss it.