Kokiri

Ocarina of Time
The Kokiri (コキリ Kokiri) tribe is a group of children-like beings that live under the leadership of Mido and the protection of the Great Deku Tree in the hidden Kokiri Forest, deep within the Lost Woods of Hyrule. The Kokiri dress in Kokiri Tunics, and have guardian fairies which look over them and seem to be a gift from the Great Deku Tree to the Kokiri. Link's mother brought Link to the Great Deku Tree when he was a baby, and asked it to care for him. After Link's mother passed away, the Great Deku Tree decided to raise the Hylian baby as a Kokiri.

The Kokiri were created by the Great Deku Tree and therefore, their homes are built not too far from him. It was said that the Kokiri die if they leave the forest. However, at the end of Ocarina of Time, the Kokiri are seen in Lon Lon Ranch along with other characters to celebrate Ganondorf's defeat. Because of this, it is theorized that the story is of metaphorical nature. If a Kokiri leaves the forest, they do not die immediately, but might be killed without the protection of the Great Deku Tree, and therefore eventually die if they do not return.

The Kokiri appear predominantly in Ocarina of Time, and return in The Wind Waker as the Koroks. While the Kokiri have bodies resembling Hylian children, the Koroks have wooden bodies and are roughly 1/3rd of the Kokiri's height. Both are mentioned to be children of the Deku Tree, strangely; the Koroks can leave the haven that the Deku Tree resides in. The Kokiri can not leave the Kokiri Forest. Note that is only speculated that the Koroks are the evolution of the Kokiri. There is no way to prove or disprove this theory.

The Wind Waker
The only known Kokiri in The Wind Waker is Fado, the Sage of Wind.

Trivia

 * The lumberjacks in A Link to the Past are sometimes thought to be Kokiri.
 * The symbol of the Kokiri can be seen in Twilight Princess on the doors of the Forest Temple and on the arm of a monkey.