Hi again Stefanie! Your kids are so fortunate, as they are at ages where they can have fun in three of Disney's fabulous Youth Clubs when you set sail on the Fantasy! As you mentioned, your younger son, is most likely able to hang out in Edge with his sister, however, since technically the age for Edge is 11 - 14, you'll need to clear this with the counselors during Open House at Edge that first day. Most likely, he'll be able to do so since he's so close to the cut-off, and since his sister will be there.
That means that they can both enjoy
Edge, the tween club, but if they see that there are activities or events taking place in the
Oceaneer Club or the
Oceaneer Lab (for ages three through 12), they are welcome to head there to join in as well! Lucky kids!
Just keep an eye on your Personal Navigator each day. This schedule of the ship's events and activities will have lines dedicated to each club so they can plan their days. My family and I like to bring a different colored highlighter for each family member so we can mark up our Navigators the night before and plan out our days.
Have so much fun on the beautiful Disney Fantasy, Stefanie! Tell Captain Mickey I said hello!