Walt:
I am not too sure what Pre-registration gets you, other than to be able to print out the forms already neatly filled out.
Younger kids (I think it's under 12, or maybe 11) have to wear a wristband while on board that identifies their muster station in case they are separated from their family during an emergency. On our cruise last December my boyfriends son Ty was given a "paper" one (same material that they used for the luggage tags they used to send out) during the muster drill. He complained that it was very uncomfortable and scratchy. (it didn't look very comfortable to wear for a whole week.)
We saw a lot of other kids who were wearing nicer, thinner plastic/rubber ones. We were told that those came from camp carnival.
Since we were traveling with the extended family, Ty wasn't interested in going to Camp Carnival, so we never registered him, but we asked if we could do it (second day) and get a nicer band for him, and they said no. (no to the being able to get a nicer band, not to registering for camp. I think he could have still signed up.)
So I think that doing the pre-registration should get you the nicer wristband - I registered my two nephews already for our cruise in TEN DAYS (yipee!). You might get the nicer band if you register when you first board - I don't know for sure. Maybe someone else does.