As no on else has responded to your question as yet I can do a basic response which is that we were on the ship 2 weeks ago (without children) but met a couple with 3 (ages 11, 12 and 15) and they (the children) were having a great time with lots of organised events ( and so were the parents for that matter!). They said there were 170+ children on the ship so if your trip is anything similar I am sure your son will find friends and have plenty to keep him occupied. We had different ports of call so I can't help much with trips but I would say that Rome will be very hot and not much fun for a 12 year old. At Santa Margarita you could take a boat trip to Portofino (there is a regular service from the jetty). For anyone else responding, the other ports of call are Ajaccio, Villefrance and Mahon. Hope this helps.