Hi Lisa
We got back from our second 7day Disney Magic cruise a couple of weeks ago, although our second
Disney cruise it was our kids (5, and 7) first cruise.
We all had such a great time that we've booked again for this coming January

.
The kids clubs are just fabulous, our kids didn't want to leave and they're open from 9am till 1am (they even feed the kids from their own buffet, some nights we couldn't get them to come out of the club to have dinner with us) so we really enjoyed some quality adult time
The show all the kids put on on the last day in the main theatre brought a tear to my eye, our kids and Mickey on the same stage.
The food was fabulous and never ending, and the shows broadway quality, however with so much going on I wouldn't call it a relaxing trip, Disney have a great program of events happening all day and night, some not to be missed.
Personally I'd say go for the 7 day if you can afford it, it gives you much more time to explore eveything on board and you get down into the Caribbean.
Give me a shout if you want any more info.
DAve