We LOVED late seating. Our DS was 5 for our cruise last fall. Since we were spending most of our days with him (unlike home) we let him choose whether he wanted to dine with us or not. He only came to the dining room with us once - every other evening he chose to go to the club. Since a long, "restaurant" dinner isn't most kids favorite (although the servers do liven it up some for them) letting your oldest (and maybe your 3 year old) go to the lab/club while you dine might make for some pleasant dinners for you!
Another "plus" of late seating is that you see the show EARLY. Our son really enjoyed the shows with characters (Golden Mickey's, Disney Dreams & Hercules) and I'm not sure he would have been as awake if we had to see the late show.
If your kids go to the lab/club - they can either eat there (a set time - actually before even early seating) or you can get them something from Plutos or Room Service. Our DS loved getting room service and would eat while DH & I were getting cleaned up for dinner.
I hope this helps,
pdarrah