According to officials, the family of 22-year-old Danielle Son had not been in contact with her since February 17 and found her children, aged 11 months and 2 years, alone in Son's home.
The family could not locate Son and contacted police.
In the ensuing investigation, detectives Son's boyfriend, Sergio Quiroz, and her estranged husband, Hand Son, were also found to be missing.
Hand Son's white 2007 Toyota Sion has also been reported missing. The vehicle has red rims and the Illinois license plate number 915407.
Authorities said foul play is suspected in all three disappearances and all three subjects are thought to be in danger.
Anyone with information is asked to contact Rockford Police.