Young Link, known in Japan as Child Link (こどもリンク, Kodomo Rinku), is the child version of the adult Link. He's notably smaller. Being brave and gentle like his adult counterpart, he's often trying to save innocent people from danger. He was a playable character in Super Smash Flash but, along with InuYasha, Mr. Incredible, and Mega Man X , was cut from the roster of Super Smash Flash 2.
In Ocarina of Time, Link lived in the Kokiri forest for the majority of his life until the Great Deku Tree called him forth by sending him his first companion fairy called Navy. Eventually, Link finds out that the Great Deku Tree had been poisoned by a magical wizard by the name of Ganondorf and heads out of the woods leaving the forest behind for the first time. Upon finding the Temple of Time, Link realizes that the door leading to the Master Sword is shut and that he must gather all three spiritual stones in order to open the door. When Link finally gathers all three stones and grabs ahold of the Master Sword, he is stuck in time due to the fact that when he pulled the Master Sword from its pedistal, he was too young to become the Hero of Time. Link was stuck holding the Master Sword in his hand for seven years in which during that time, he became an Adult. It was at that time that Young Link referred to the Link seven years in the past while Adult Link meant the Link from seven years into the future.