When Gohan asks how his transformation occurred, Goten said that he was learning Martial Arts from his mom and she told him to never turn Super Saiyan again. Goten transforming into a Super Saiyan made him the youngest Super Saiyan ever at that point. Chi-Chi first discovers that Goten can become a Super Saiyan at only seven years old, he looks almost exactly like Goku when he first transformed into a Super Saiyan.
Goten is incredibly strong as a child, far stronger than either Goku or Gohan were at his age. The reasons for this are never fully explained, but it seems to have something to do with Goku's death. Goten is not pushed in school as much as Gohan is and instead is trained in martial arts by Chi-Chi. Goten is born shortly after the Cell Games Saga, and had not met his father Goku until he reached the age of seven. Goten is the second son of Chi-Chi and Goku, and younger brother to Gohan. He also shares the typical Saiyan appetite like his father and his brother. Towards the end of Dragon Ball Z, Goten is seen with a shaggier hairstyle. However, Goten's appearance drastically changes as he grows older, resembling his brother Gohan more than his father as a teenager, he has the same long messy hair as Gohan at a younger age.
Goten's appearance is very similar to Goku's childhood look, including messy, unkempt hair and a playful face. Goten is seen sleeping in his crib, surrounded by family 3.1 Search for the Black Star Dragon Balls.