31-year-old Charles Douglas Scaggs III has been identified as the suspect involved.
A 24-year-old woman and her 3-year-old nephew were approaching a McDonald's near 35th Avenue and Van Buren on April 28 when Scaggs reportedly assaulted the woman and grabbed her purse.
The woman had been holding the little boy, and the attack caused them both too fall.
Phoenix police spokesman James Holmes says the boy's face hit the ground, pushing his front teeth into his gums.
A Good Samaritan saw the alleged attack and ran after Scaggs. He was able to get the purse, but Scaggs got away.
The 3-year-old had to have two teeth removed as a result of the fall.
Officers began to pass out surveillance photos of the suspect around the area hoping to identify him.
On May 31, police received a call saying a person making the suspect description was inside a Circle K near 43rd Avenue and Van Buren.
Officers spoke with Scaggs and Holmes says he later admitted to committing the strong armed robbery and aggravated assault during an interview.
He was booked into jail.