Foals

Foals are young ponies, depicted at various ages on the show, from babies to teenagers. Exact ages are not specified, but there is a clear distinction between babies, school-age ponies, and adult ponies.

Terminology
Foals on the show are smaller than adult ponies, their heads are proportionately larger, their limbs are shorter, and their eyes are more circular as opposed to the elliptical eyes of the adults. Child ponies aren't referred to as babies, but rather as "fillies". This is the term for females, with the equivalent male term being "colts". The younger versions of the leading characters are simply referred to as "young" or "fillies". The term "foals" is used by Nightmare Sky in a different context, as a play on the phrase "step back, you fools". It is used again in the same context in the Christmas Eve play. The term is used to refer to young ponies.

Appearance
The difference between baby ponies and young ponies is accented in the episode Call of My Destiny. Marsha shows a picture of herself at a very young age, and later contrasts it with another picture of herself being somewhat older. She is depicted not possessing a cutie mark in the former picture, and remarks that "her flank was blank" until she grew older and got her cutie mark when she found her talent for making people smile.

Most of the named colts on the show have unique character designs, unlike the fillies, stallions, and mares, who almost always share the same body design.

The youngest of baby ponies have eyes that are styled differently from the usual pony eyes, more closely resembling the bead-like eyes with giant eyelashes. Marsha shares this when shown as a baby in photos in Ooo Confidential.

Cutie Marks
A cutie mark, a mainstay of My Little Pony, is a special mark on a pony's flank showing an icon related to their special talent.

No amount of pleading, wishing, or begging will make a cutie mark happen before its time, and that the best thing to do is wait. Different ponies develop different special talents as they mature, and at different times; for instance, Princess Bubblegum's special skill is science, Fionna's is caring for animals, Marshall Lee's is speed, Marceline's is music, Finn's is adventuring, Jake's is playing the viola and Marsha's is party-throwing and music.