The boy boarded a Jet2 flight yesterday afternoon (July 24) having evaded five different security checks, the Manchester Evening News reports.
The child ran away from his mother during a shopping trip to the nearby Civic Centre in nearby Wythenshawe and was even scanned at security in Terminal 1.
He then boarded the plane to Fiumicino airport, and passengers became suspicious after the flight had taken off.
Five members of staff are believed to have been suspended while an investigation takes place, and the boy was flown back to the UK on the return flight.
"This extremely serious matter is now being urgently investigated by officials from the airport and airline," an airport spokesperson told the paper. "It is clear that documentation has not been checked correctly at security and the boarding gate.
"The boy went through full security screening so the safety of passengers and the aircraft was never compromised. We are now making preparations to ensure that his return to the UK is handled sensitively to avoid any distress."
A Jet2 spokesperson confirmed that the airline was aware of the incident, which it is investigating as "a matter of urgency".