The security mishap happened Thursday at the airport, KARE-TV, Minneapolis/St. Paul reported.
The boy, apparently a runaway, entered the airport Wednesday night and slept in the terminal.
He then managed to board Delta Flight 1651 to Las Vegas on Thursday, without a boarding ticket, and wasn't stopped or questioned until the plane landed.
Delta officials said, "We are investigating the incident and cooperating with the agencies involved." The Transportation Security Administration released a similar statement.
"He had to pass three levels of security," said Terry Trippler, an air travel expert with ThePlaneRules.com. "You have the TSA, the gate agents, and the flight crew and a child comes through without even a seat assignment."
"While we are safer in the air, this proves there are still gaping holes," Trippler said.
Minneapolis airport spokesperson Pat Hogan said the boy is being returned to Minnesota.
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