Cruising entertainment and enjoyment is what you make of it. Some of us enjoy the food, casino, lounging by the pool, the dancing and festive music, etc.
It really depends on what you enjoy. I will make one suggestion that pertains to your 7 year old. Carnival has a kids' club that my children, now older, used to ejoy totally. The first ten minutes were a little akward for them because they didn't know anyone, but after a short period I couldn't get them to leave.
my first cruise I didn't see my twins except at meal time (and even then sometimes they chose to eat at Camp Carnival) and of course at bed-time. My only complaint with the kids club is that when you take your child there for the first time they will not allow the parents to come into the kids club area, if even for a few min's, so that you can see first-hand that your child feels comfortable there. Don't get me wrong -- I'm not an overprotective mom but my kids accept changes and strangers better if Mom can sit in the room for a few min's until they check things out and decide it's a cool place to hang out. But they do give the parents a pager that they use to notify a parent if the child decides that they want to spend some Mommy/Daddy time instead of hang out with the kids' group and activities.
One other thing I learned... On my first cruise (not a Carnival ship) I purchased two-way radios for every member of our trip (all 8 of us). This was great because I could let my older kids have run of parts of the ship and could radio them from time to time to check on there location and activities. But on Carnival (at least on Fascination) the two way radios didn't work at all.... We had to be more creative with the oder kids -- tell them to meet us (parents) at designated times every hour or two just to check in.... It worked but it was a little worrisome going two hours without hearing from my twelve year olds.
Good luck, and have fun. If you can do a lil' research on Carnival's website and message boards you'll be able to familiarize your seven year old about some activities (kids club or with parents) that they will want to try. Also look for info. that relates to small children as well. I'm sure that there's things to do that can be enjoyed by both adults and smaller childdren as well!!