Christopher Kuhn, of Hamilton, New Jersey, is charged with third-degree murder, homicide by vehicle, retail theft and related charges.
Police say Kuhn was fleeing a department store in Tullytown, Bucks County, with stolen goods early Tuesday afternoon when the crash happened.
They say he stole speakers for a television set from a Walmart store and was attempting to get away from the scene with his son in the back seat.
Authorities say Kuhn ran a red light at the intersection of Route 13 and Levittown Parkway.
Child Dead After Suspect Crash
Fernando Medrano, who had a green light, T-boned Kuhn's Jeep SUV, causing it to collide with another vehicle.
"I tried to brake, but I couldn't," Medrano said. "It was too late. He was moving too fast."
Kuhn's SUV flipped on impact and rammed another car traveling north on Bristol Pike.
Police: Toddler dead after theft suspect crashes SUV during getaway
The 2-year-old child in the SUV was thrown from the vehicle during the collision. He was rushed to an area hospital but did not survive.
Police said Kuhn ran from the scene of the crash, but he was captured by police a short distance away.
"I saw it when the baby flew, and I saw Kuhn run away," Medrano said. "I just can't believe he ran away."