Authorities in California are searching for an elderly woman and her two young grandchildren who mysteriously disappeared this week.

Sandra Young, 75, of Fairfield, California, and her two grandchildren, 9-year-old Jayden Hill and 7-year-old Katalyhah Hill, have been reported missing by family members. Young last spoke with her sister on Sunday. Relatives haven’t been able to get in touch with her since, according to a press release from the Fairfield Police Department.

Young’s car, a green 2000 Acura TL with a California license plate, isn’t at her home. Although her current location is unknown, Young is believed to be in the company of her two grandchildren, police said.

Young and the children are considered to be “at risk” due to their ages as well as Young’s medical conditions, police said. It’s unclear what medical conditions Young has.

Anyone who thinks they have seen Young and her grandchildren, or has information on their whereabouts is urged to call 911.