His parents dropped out of Hogwarts to get married and have him in 1845. His mother took care of him for the first two years as his father finished his education.
When he was 6, his father died while his mother was pregnant with Iola. One day in 1853, he was playing outside and made a stone move, proving his magic to a couple of muggle neighbours. The boys were scared and tied Sirius up, pushing him in a river to test if he was able to survive that and drowned, not able to control his magic fully. His death resulted into a hatred of muggles for his brother and sister.
Sirius was a handsome boy that resembled his father but younger and happier. He had his mothers smile.
Sirius was playful and cheery and the joy in his parents's lives.