An 11-year-old boy flew to Rome from Manchester Airport by himself without a passport or boarding pass.
Liam Corcoran passed through security without being checked, before making his way on to the Jet2.com flight yesterday.
A Manchester Airport spokesman said: "This extremely serious matter is now being urgently investigated by officials from the airport and airline. It is clear that documentation has not been checked correctly at security and the boarding gate."
More top news
Striking rail workers and engineering works are set to cause a headache for many Britons travelling over the bank holiday weekend.
An eight-year-old boy has been caught on camera going for a joyride with two other young children in the car.
The law should be changed to allow assisted dying, the country's former top lawyer has said.