Stalchild

The Stalchildren, also known as Stalkin, are skeletal nocturnal enemies that rise from the earth immediately after sunset in Ocarina of Time and Majora's Mask, and in dungeons in Twilight Princess. These beings commonly group in packs of two, though not always. They are relatively easy to defeat, requiring only a couple of sword slashes. Even the largest versions that appear over the expanse of Hyrule Field in Ocarina of Time can be killed this way.

Captain Keeta from Majora's Mask is the most notable Stalchild to date.

Ocarina of Time
Stalchildren can be seen roaming the fields of Hyrule at night in Ocarina of Time. They pop out of the ground, walk slowly toward Link, and attempt to slash him with their claws. They are quite easy to kill, and if Link destroys enough of them in one night, a larger one will pop out; if it is defeated, it will give a larger Rupee reward than the others.

If two of these larger ones are defeated before dawn, an even larger one will appear. To prevent their appearance altogether, put on the Bunny Hood before nightfall or simply stay on the dirt roads. Each time Link kills a certain number of Stalchildren, they can grow to a size similar to Captain Keeta from Majora's Mask. Once Link becomes an adult, these creatures mysteriously disappear.

''Majora's Mask
In Majora's Mask, the Stalchildren are of the Ikana race. In the game, they haunt the Ikana Graveyard and are the fallen soldiers of the Ikana Kingdom. Their general is Captain Keeta, but they'll mistake anybody that wears the Captain's Hat for their fallen leader. By wearing the Captain's Hat, the Stalchildren will ask Link whether they should open or guard the grave, mentioning that they already had an order from Captain Keeta to guard it. While this is their most major role in the game, they also have a slight role in the Oceanside Spider House, where each of the Stalchildren in there will reveal the solution to the house's puzzle, ultimately leading to a Piece of Heart.

Twilight Princess
Known as Stalkin in Twilight Princess, they are miniature skeleton enemies similar in appearance to Stalfos found in the Arbiter's Grounds and the Cave of Ordeals. Stalkin emerge from the ground in large groups and attack with small tridents. While individually they are weak, they can be quite bothersome in packs. They can be destroyed with almost any weapon, though Link's sword is arguably the most effective for dealing with large groups of these tiny nuisances, especially when the Spin Attack is utilized.

Theory

 * Stalchildren are considered to be younger versions of Stalfos in Ocarina of Time and Twilight Princess. The only other explanation hinting towards their relation to Stalfos is their ranking in Majora's Mask, appearing as footsoldiers as opposed to the Stalfos-like bodyguards in Ikana Castle. It should be noted however that at least one, if not all, Stalchildren in Majora's Mask are adults. There is also the fact that Stalchildren don't appear when Link is an adult, in Ocarina of Time.
 * In Ocarina of Time, it is theorized that something could have wiped them out during the seven years after Ganondorf took over Hyrule. The logic of this occurrence is often argued, as it is widely thought that the Stalchildren should have flourished under the rule of Ganondorf. Due to the speculation tying them to younger versions of Stalfos, they could have just grown up as Link did, becoming their sword-wielding counterparts Link faces later in the game.
 * It is also possible for the Stalkin to be the dead remains of the Miniblin as both wield tridents, are relatively small, are easily defeated, make high pitched noises and appear in large hordes.