This kid? He looks kind of scruffy.”— Daxter
The Kid is the son of Damas and an unknown woman, and the heir to the throne of Haven City. At some point prior to Jak II, he was kidnapped by Count Veger, who had intended to harness young Jak's Eco-channelling abilities for his experiments. Though Veger claims that he "lost you [Jak] to the Underground", the Shadow says that he found the Kid "just wandering the streets", suggesting that young Jak may have escaped from Veger under his own power.
Though the Shadow was the one who found the Kid, throughout the game he is mostly seen under the watchful eye of Kor. His only other companion during this time was his pet crocadog, who appeared to hate everyone but the Kid and Jak.
The Shadow had originally planned for the Kid to open the Tomb of Mar and pass the Trials of Manhood to gain the Precursor Stone in order to defeat the Metal Head Leader, but the Tomb refused to admit the Kid on the grounds that he was too young to face the tests. After Jak passed the trials, the Kid supposedly vanished; in fact, Kor had kidnapped him so that he could open the Precursor Stone.
After Metal Kor's defeat, the Kid was sent back to Sandover Village with Young Samos using the Rift Rider that Keira had built. Before leaving, he gave his Seal of Mar pendant to Jak after being warned to stay away from wumpbee nests on his ninth birthday.
He appears briefly in a flashback during Jak 3, when Damas charges Jak with finding his son, Mar. When Damas was dying under the weight of his overturned Slam Dozer he told Jak that his son would be wearing the Seal of Mar, which Jak remembered his younger self from Jak II was wearing. Meaning that he himself was Damas' son(Mar)and Damas was his father (with his mother still nowhere to be found or mentioned). However Damas died before Jak could tell him he was his son.