small horse; pony
Refers to a horse of small stature, including ponies. Not necessarily a young horse.
There are several small horses at that farm.
foal; colt; filly
Specifically a young horse, typically under one year old. Colt is male, filly is female.
The foal born in spring is running around energetically.
Standard kanji spelling for a young horse.
Alternate kanji spelling; 仔 also means young animal.
Alternate kanji spelling; 小 means small.
Compound of 子 (ko, 'child') and 馬 (uma, 'horse'), with rendaku voicing of the second element.