I would imagine there would be consequences for Jet2 of some kind if they off loaded a child of 11 suffering from learning difficulties in Rome and left him there. Yes, the child in question suffers from learning difficulties.
A number of points
1) the crew were not to know that the child had learning difficulties. He clearly had the wherewithall to get onto an international flight without any documentation whatsoever
2) once handed over to the Italian authorities, the British Embassy would then have to look after the child's welfare, including his repatriation. After all, he was seeking adventure so why not add to it by handing him over to the Italians
3) what if the flight was full for the return to Manchester? Should the company offload a fare-paying passenger for the sake of an attention seeker?