Passengers under 14: under no circumstances they can travel alone without the accompaniment of an adult. Furthermore, if the adult in question is not one of the 2 parents, a letter of trust is to be handed over to the Master of the vessel/Purser in which the parents declare that they entrust their child to the designated person, who will be responsible to all effects of the law.
Valid identity documents of both parents must be attached to this letter. If they are people who come from outside the European Union, the parents’ residence permit showing the details of the child must be attached thereto.
For passengers under 14 years of age with Italian citizenship, traveling on international routes, the accompanying declaration filed with the police headquarters is required.
For further details regarding the procedure, you can contact the police headquarters of reference or consult the following link https://www.poliziadistato.it/icle/191.