Hi RTM,
I just got off the Magic with our twin 7 year old sons (and DS12 and DH).
We did Eastern, because I wanted the extra day at sea. The kids enjoyed the clubs (but preferred the pools!). Our St. Maarten excursion was cancelled (Golden Catamaran snorkeling) at the last minute (due to high seas conditions), so we hopped on the water taxi and spent the afternoon at Great Bay beach. The kids had a blast on the water trampoline there. (thank gawd I had read these boards so much and so was quickly able to come up with a "Plan B"...it turns out we absolutely loved our day on St. Maarten, so we weren't heartbroken over our cancelled excursion). On St. Thomas, DH took the twins on the submarine excursion (which they really enjoyed) and DS12 and I shopped a little (no big deal, but it was nice that we had some time together). On both these days we enjoyed the pools on the ship with the kids- alot less crowded on port days!
If you aren't especially interested in a particular port of call, consider
DCL's "special" itineraries with 2 days at
Castaway Cay.
Remember, if you do like a particular port/excursion, you can leave the children on the ship if the excursion isn't appropriate for their age. But if you think you will be doing 7 year old stuff mostly, you might find that what they really love to do is hang out by the Mickey pool, eating ice cream from Scoops!
Hope this helps a little! Happy Planning!