Hi Pettygirl,
My kids have been cruising with us for year and love the kids clubs. I have a 13 year old and 7 year old currently but they both started going to "Boat School" as they dubbed it when they were 4. For the 6 year old age group, go to the kids areas right away and get them on the list (as you said) you should also sign the waiver on the cruise presonalizer to get them preregistered. They will put a kids patter in your room the first day with events/parties/dinners ect. for the whole cruise. You will also get to decide if the kids can check them self into and out of the kids club. We have never used the afterhours babysitting but they do usually have 2 nights per cruise where they have a dinner/dance/pj party during dinner time to give the parents a way to enjoy formal nights. They will have themed days/nights with games, crafts and video game tournaments. My kids also love to go to the t-shirt making and stuffed animal making events each cruise. When we were in Alaska they even brought a naturalist onboard to talk to the kids about Alaska and the different animals and climate. Let me know if you have any questions, i'd be more them happy to answer whatever. As my kids have gotten older they seem to use the kids clubs more and more often.