We just did Christmas -- most of us had teens, one family had a 10 yo girl, and another an 8 yo boy.
There was a lot of variety as to how this was handled. Several families had "Christmas" with relatives before they left. Several families are waiting until they get home.
DH and I gave this cruise to our family as its Christmas present this year - but the girls got stockings with really nice things in them -- Disney dollars, disney pins (special for the 2003 Christmas Cruise, and Mickey's Very Merry Christmas Party last night event pin), lanyards (Pretty Bunny and Care Bears), and a Magic Sterling silver charm for their charm bracelets. I also brought some Ghirardelli chocolates, some flavored lip balm, a tooth brush and a pair of Christmas panties (there are some traditions you just cannot break).
Each DD got one thing they had mentioned time and time again and I knew they really wanted (small things, video game, cotton zip up jacket from the Wet Seal), and they each got a DVD - Finding Nemo and POC. These four gifts were each placed in a small lunch bag sized Christmas gift bag (these packed really well, with the tissue folded inside them). We did decorate our cabin with a 3' christmas tree with lights, garland and ornaments, red and white lights hung around our porthole, and decorations on our door. I didn't decorate the house for Christmas, as we left on the 17th, and therefore couldn't find their stockings at the last minute. We found really cute larger sized gift bags with Santa Mickey on the front at the Target in Kissimee, which we used as their "stockings". I put everything around (not enough room under) the tree early Christmas morning (had everything prepared Wednesday afternoon and stashed in the closet).
I carried all of these gifts, the bags, tissue, and candy in my carry-on. I also, unbeknownst to me, had a very small 8" metallic red flash light in my bag, which got the airport security in NC into a frenzy immediately - so the bag was searched, but the airport employee was very nice about making sure everything stayed in its respective store plastic bag, and he just looked and pawed through everything. I later took the flashlight and placed it in the zip pocket at the upper opening edge of my carry-on bag, and warned all the security beforehand.
We were told before we left by the CM helping me with our excursions 60 days out that if we brought Christmas presents onboard (I believe in carry-ons) that they would be unwrapped and examined. We all either had them unwrapped as I did, or wrapped and in the checked baggage.
I hope this long-winded post answers your questions!!
It really depends on your children, whether they can handle Santa finding them somewhere else (when ours were younger and we would have Christmas with relatives, we made a big production of writing to Santa around 12/15 - letting him know where we were going to be Christmas Eve, so he could find us). Now that the girls know the truth about Christmas Magic, they are more than happy to spend their Christmas on the Magic, and do without so many presents!!