A nine-year-old Minneapolis boy was able to get through security and on a plane at the Minneapolis-St. Paul International Airport without a ticket.
Metropolitan Airports Commission spokesman Patrick Hogan said security screened the boy at the airport shortly after 10.30am on Thursday.
He then boarded a Delta flight that left for Las Vegas at 11.15am.
Mr Hogan says the flight crew became suspicious and contacted Las Vegas police, who met the crew upon landing and transferred the boy to child protection services.
Delta and the Transportation Security Agency released statements saying they were investigating.
Mr Hogan says the boy is expected to return to Minneapolis-St Paul.