Greek minors under 18 years of agewho travel from Greece without their parents or legal guardians should bring with them: (i) a valid passport or (ii) a National ID issued by the government, together with a written permit signed by the parents or legal guardians. This permit should be certified by the Greek police.
In any event, they will be asked to prove their age.Therefore, they will have to present valid travel documents at the boarding gate.
Greek minors under 12 years of age travelling with their parents or guardian on a domestic route can travel with the health booklet or birth certificate (even no picture included).
For more details, please visit this page.