Jeffrey Anderson said his granddaughter, Trinity, apparently was shocked after placing the cable into her mouth, suffering third-degree burns to her lips, palate and tongue, The Daily Camera (Boulder, Colo.) reported Thursday.
Anderson said the cables, which typically carry five volts of electricity, could pose a danger to other children.
"With the number of people who have these, with the number of doctors and nurses who say they've never seen anything like this, we felt we had to let people know," he said.
Anderson said the young girl's mother was using the laptop computer at the time of Monday's accident and immediately rushed the girl to the hospital.
The Daily Camera said medical staff are using sedatives and paralyzing drugs to restrict the infant's movements and will assess possible neurological damage after allowing the child to regain consciousness in coming days.