I will try and help save CM_Mom's typing fingers but answering what she would most likely answer.
The CMs in the club and lab are very accomidating and are there to make sure you and your children have a magical and wonderful vacation. Just talk to the CMs and tell them you situation and they will most likely allow your five year old to move up on a trial basis. However the CMs will not allow a child to go back and forth, so he/she may say go with the 3-4's for one activity, then to the 5-7s for another, and then go back to the 3-4s.