FBI Minneapolis agents and state law agencies are stepping up their search for Daniel Hauser.
A federal warrant says Hauser and his mother left Minnesota on Tuesday on a Sun Country Airlines flight to Los Angeles.
An FBI affidavit was filed in U.S. District Court on Friday, alleges Colleen Hauser fled Minnesota to avoid being prosecuted on two counts of depriving another of custodial or parental rights.
The paperwork gives the federal government jurisdiction to assist in finding and arresting Hauser on the state charges.
Interpol, which coordinates police investigations across national borders, was joining the effort to find Colleen and Daniel Hauser.
"We're putting every effort we can into this," said Jason Seidl, a sheriff's deputy in southern Minnesota's Brown County.
The pair were last seen Tuesday morning in southern California, before authorities in Minnesota even realized they had left the state. Investigators suspect they might have headed to one of a number of alternative cancer clinics in northern Mexico.
Their current whereabouts are unknown.
Daniel has Hodgkin's lymphoma. A judge has ruled that if found, he will go to a foster home so he can be treated for the disease.
The Associated Press contributed to this report.