first time cruiser-with-kids questions

Help!
My husband and I are trying to plan a nice family vacation and are looking into cruising (we've never cruised individually, let alone with kids).
Our (sometimes very active) boys are 2.5 and 5.5 years old. The younger is not yet potty-trained and loves to be with his big brother (not in a nursury).
I'd love any advise from anyone who has traveled with little ones - i.e. which line is best for the (un-potty-trained) toddler? Is there anyway the kids could wander off and fall off the ship (sorry, I know this is crazy, but I tend to worry)? Would a 4 or 7-day cruise be better for their age? Should we upgrade our cabin (from inside to outside or even balcony staterooms)?
Any other thoughts/advise would be welcome as well! Thanks so much!!!

I'm the family cruise editor here. The only lines that accept kids under three in the youth programs are NCL and Carnival. While Carnival's youth counselors change diapers, NCL's will beep you to come and change the diapers when necessary. (ON NCL, you can't go off the ship if your little one is in the youth program in diapers.)
I prefer 7 day cruises since it always takes kids a few days to get used to a new atmosphere and after a few days, they think of the ship and your cabin as home. The ships are very safe -- we've been on 12 family cruises without a problem.
Balconies are great if your younger one still naps in the afternoon because you can sit on the balcony while they snooze inside. It's just more challenging to keep the door locked for safety reasons with a pre schooler.
Feel free to ask more Q's. I think you'll really like cruising with your kids!
Smooth sailing,
Luisa Frey Gaynor

[LisaK]

also consider Disney Cruise Lines.

Thanks Luisa!
I appreciate the input as well as all the other info I found in your articles. This is such a great website!!!
Thanks again!

Thanks for the compliments! Let us know what you decide -- which cruise line, etc.
Smooth sailing,
Luisa Frey Gaynor