Don't be nervous..You may never see your 7 year old..SO much to do for kids. Husband and I went on Disney cruise little over 3 years ago with no kids. They will give you a pager when you drop off your son for activities..Pagers are expensive (I think $175)..DON'T break it.
On Disney cruises all food and soda is included in price you paid for cruise. There is no casino's on ship..They do offer bingo on ship cause it's something kids can do and kids enjoy bingo..IF kids win an adult needs to be with them to claim cash. I can't remember cost of anything..Memory must be shot!!
Castaway Cay was a BLAST..Have sections for families, one for teenagers and adult only. We spent all out time in adult only section..So I am no help to you..BUT did look like they had a ton of activities for all ages.
We did not like Nassau..We spent that day on ship..Was our "movie" day..Any Disney movie that premier's (speeling off) also premiers on ship.
Any other questions I will try to help