Welcome Aboard, Shelly!
I'm so glad you asked this question! I have a daughter who'll be visiting the Edge tween club on our next cruise, and this was something I also wanted to know.
When you visit Disney's private island,
Castaway Cay, you'll find fun activities throughout the day for all ages! As you mentioned, the youngest cruisers can be checked in to Scuttle's Cove, and the teens have Teen Hideout and a Port Adventure option just for them. For the tween set, most organized activities will be held in the "In Da Shade" pavilion located near the Family Beach.
On a recent cruise, tweens had the following activities listed on the Personal Navigator (a daily schedule delivered to your stateroom):
*Sand Soccer
*Hangin "In Da Shade"
*Lunch at Cookie's BBQ
*Pelican Plunge
*Invade Teen Hideout
The Edge Youth Counselors will be on hand at these scheduled activities, but you won't have to check your child in and out like you do for Scuttle's Cove. I plan to walk my daughter to the area of the activities she's interested in, then come back for her when she's finished (if it's far from where we've settled in for the day).
Hope this helps! Thanks for visiting the Disney Parks Moms Panel - please let us know if you have any more planning questions.
Have a magical day! - Diane W.