They check each person to ensure that they have a room key and then issue you a bracelet. We have family visiting us from Tampa when we were down and they were NOT allowed to enter the pool area. We had to leave that area and meet them in the lobby. We asked the guy checking cards if they could sit by the pool and chat with us while my 2 year old went swimming and he said no. We were happy they were so strict and just got dressed and headed to the boardwalk to hang out!!
I know he won't be able to go to SAB with you, but you should be able to visit the villa pool together. No one checks keys there and there is easy access from the villa lobby.
We stayed at VWL and had our friends from Daytona visit for the day. We sat at the pool area without a problem.
Ya, as the PP said, you could add your nephew to the list of people occupying the room and get a room key for him when you check in just as long as you have not gone over the max # of occupants for the room.
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