I just got back from Oasis of the seas on Sunday. Anyone you list when you sign your child up can pick up. My father got my kids a couple of times. When the ship is at sea, there are times the club is closed, but during port days the club was open most of the time. If the kids were still signed in at 11 or 5 they were taken to the windjammer for dinner. They also met outside the dining room at 6:40 so you could sign them into club, they were escorted back to their rooms and you could finish dinner in peace. There was a late night club that operated from 10pm-2am for at $7 an hour fee (but we didn't use it- my kids were done by 9 or 9:30). The nursery (ages 0-2) was available at $6 an hour until 6pm and $8 an hour then until midnight. You could reserve 15 hours in there for the entire cruise up till day 3. Then the morning of day 3 you could book as much as you wanted. We used our hours to secure the evening times, as they were the most popular and they only had 8 spots per hour.
My two oldest (ages 5 and 6) LOVED the club and begged to go each day. They did games, sang songs, did crafts. They painted the kids faces a bunch of times, and there were two shows that the kids performed for the parents. The older kids had a parade around the promenade one night. My youngest (3) was not as enthusiastic and sometimes wanted to stay with us, but he was always laughing and having fun when we came to pick him up. They all came to know all the staff members by name and would greet them as they saw them around the ship. They knew my kids too, and would call them by name. My older was in the Explorers room and the other 2 in the Aquanauts. They got their own cruise compass in the room each night and each session had a theme. There were a BUNCH of kids in the Explorers room (sometime 40 or 50 kids) but it also seemed 'organized chaos' and the staff members could (and did) get everyone quiet almost instantly with a special chant. There seemed to be a good mix of structure and free fun. There was also a science and art lab that the older kids got to use. The younger room had a lot less kids (the most I ever saw in there was 15-20) and I saw them reading books to the kids several times when I picked up.
I was pleased with the Club, (especially that my kids wanted to go so we could get some adult time) and we will continue to sail with them in the future.