Investigators say Shyanne Charles and Joshua Yasay, 23, were innocent victims of what appears to have been a gang shootout that also wounded 23 people, the Toronto Star reported.
Shyanne's grandfather, who joined a community vigil Tuesday night, urged witnesses to speak out and young people to give up guns.
"This child should be an eye-opener, a wake-up for the whole community," Tyrone Charles said.
Yasay, an Ajax resident who graduated from York University last year with a degree in criminal justice, had opened a barbershop, Goodfellas, with a friend while also working as a security guard. He also volunteered in a basketball program for at-risk youth and hoped to be a police officer.
Shannon Longshaw, a party organizer, was there right after Yasay was hit: "We just saw blood. He just said, 'Don't let me die. Save me.'"