Just because they're small doesn't mean they're babies.
Nothing drives an equestrian crazy faster than someone pointing to a pony and saying, "Awww, what a cute baby horse!"
While it may come as a surprise to many non-equestrians, ponies are not baby horses; they are fully grown equines who mature at a smaller height than their horse relatives.
Horses and ponies have a number of physical differences in addition to the obvious difference in height. Ponies are not only shorter, but often wider, with thicker legs and bones and a wider barrel. They are known for being shaggy, and often have thicker manes, tails, and even coats.
While various organizations recognize different heights, the most commonly recognized height for a pony is 14.2 hands and under, or the equivalent of 58 inches, 147 centimeters, measured from the withers. They are remarkably strong for their small size, and larger ponies can even be ridden by adults.
Ponies are thought to have evolved from horses making their homes on the margins of livable habitat, become smaller and hardier to survive.
The confusion between ponies and baby horses is understandable, since the word "pony" is derived from the old French word "poulenet," meaning foal, or baby horse. But if you want to impress a horse person (or at least avoid the eye rolling), point to a pony and say, "Awww, what a cute pony!"
You will immediately gain a few points in their eyes.