Carnival is great for kids. They have a program to fit just about any age rage. Just go on Carnival.com and you can look at the Camp Carnival activities under the Onboard Activities link. My kids are 7 & 9 and had a great time. I didn't have to worry about them as they were well taken care of.
Our daughter is 7 & loves Camp Carnival. She is an only child so to her this is like being in heaven. Every night when we get the Carnival Capers paper we go through it with her & she picks out the activities that she wants to join in on the next day. I think your son will have a wonderful time. Our daughter never wants to even eat with us. She always says, "I want to eat with my class."