Dr. Carol Glaser, leader of a California Department of Public Health team investigating the illnesses, said the paralysis strikes rapidly -- sometimes 48 hours after a mild respiratory illness.
Scans of patients' spinal cords showed damage similar to that of polio sufferers, but Glaser said it was definitively not polio. Heath officials do not know what is causing the paralysis, the Los Angeles Times reported.
Two of the children tested positive for enterovirus-68, a virus associated with respiratory illness but linked to polio-like illnesses as well, Glaser said.
Dr. Keith Van Haren, a pediatric neurologist at Stanford University's Lucile Packard Children's Hospital working with Glaser's team, is scheduled to present the cases of five of the children at the American Academy of Neurology's upcoming annual meeting in Philadelphia.
Glaser has been investigating the illnesses since 2012, when a physician first requested polio testing for a child with severe paralytic illness. Glaser called the request "concerning," because polio has been eradicated in the United States and none of the patients had traveled aboard.