Baby horses are called foals when they are born are usually are able to stand up and walk within a few hours.
Female horses are called fillies until the age of 3 and male horses are called colts. For the first six months or so, a foal will hang out in the pasture next to its mother, nursing and during this period horses aren’t offered for sale without their dam (or mother) and are sometimes called sucklings. After a horse is weaned from its dam, it may be called a weanling up to the age of 1 year. After that, horses between the ages of 1 and 2 are called yearlings.