I will take a try at your question about child safety.
If they are in kid's club, you will need to sing them in and out unless you give them authority to sign themselves in and out - there is a minimum age for this.
As for the rails, they generally slope inwards towards you and are about 4 feet high. We set the groundrules with oru kids on day one to not go near the rails or stand on them, etc and they never did.
I never felt uneasy except for one day when I was on deck and caryingmy three year old and realized that she was above railing height. I quickly put her down/moved further from the rail.
I do not want to tell you not to worry but we do not worry about this - cruises have thousands of kids on them every week and I have yet to hear a story about one going overboard. most who go overboard on a cruise have met with foul play or were just plain drunk and apparently not as invincible as they thought they were in this state!
Common sense and keeping as close an eye on them on the ship as you would at home should keep everyone safe and happy.
My two cents on Disney versus other. Disney will cost you much more and you will get all the Disney you want (and maybe more)...there is no way to get away from Disney on the cruise. We really enjoyed
RCCL and save our Disney time for the parks and can pay for a Disney park stay (with free dining) with what we saved by going with RCCL on our cruise.
maybe I will see you over at cruisecritic.