It occurred on Thursday just after 4:30 p.m. near 2628 Nicollet Avenue South in Minneapolis.
The surveillance video shows the man, identified as Aaron Stillday, dropping the tablet after punching the boy. The 8-year-old fell to the ground. Seconds after falling, he got up and ran back into the day care he was leaving to get help.
Mohammad Armeli witnessed the attack and tried to help.
"You just don't hit a child. You don't hit a child," he told KARE 11 news. "He punched a child so hard his nose might have broken. There was blood all over his face."
"I kept running after him. He tried to get into the apartment buildings. He tried to throw stuff away from himself," Armeli said. "I stopped him right here and said 'Hey, where are you going? He said 'I didn't do anything. I didn't' do anything.'"
Stillday has been charged with first-degree aggravated robbery.
The stolen iPad was recovered but it was broken in the fall.
Minneapolis Police Department spokesman Scott Seroka said investigators have seen an increase in theft in smart devices.
"The reason we are seeing an increase is because of the resale value of these items," Seroka said. "When people are walking around with them they are almost like a target for thieves to kind of go after."
Meanwhile, the 8-year-old is recovering and expected to be OK.
Armeli, who called 911 and helped police capture the suspect, is still angry, but he doesn't regret jumping to help.
"I couldn't believe I ran so far. I would do it over and over again," he said. "I would just not allow anybody to hit a child like that for his iPad."