Image copyright Knightscope Image caption The Knightscope robots have been taken off duty while the incident is investigated
Security robots at a shopping centre in Silicon Valley have been taken off duty after one of them ran over a toddler.
His mother told ABC News the robot had hit her son's head, "he fell down on the floor, and the robot did not stop".
The 16-month-old, Harwin Cheng, was left with swelling to his right foot.
The robot's developer, Californian start-up Knightscope, apologised for the "freakish accident" and invited the family to visit its Mountain View headquarters.
Image copyright Twitter Image caption Reporter Lilian Kim tweeted pictures of the boy's injury and the robot
It said: "A child... began running towards the machine.
"The machine veered to the left to avoid the child, but the child ran backwards directly into the front quarter of the machine, at which point the machine stopped and the child fell on the ground.
"The machine's sensors registered no vibration alert, and the machine motors did not fault as they would when encountering an obstacle."
Image copyright Twitter Image caption The developer Knightscope launched an immediate incident report
Knightscope said the 5ft (1.5m), 300lb (136kg) K5 Autonomous Data Machines, which patrols pre-programmed routes recording video in both normal and infrared vision, had, until now, been in operation for more than 35,000 hours and covered more than 25,000 miles "without any reported incidents".
Chief executive William Santana Li said: "Our first thoughts are for the family, and we are thankful there were no serious injuries.
"Our primary mission is to serve the public's overall safety, and we take any circumstance that would compromise that mission very seriously."