I can answer only 2 of your questions.
I have seen kids with nice shorts and a shirt (not tshirt) at dinner. (of course not on formal nite).
Kids do not have to order from the kids menu. My kids never do. They always order seafood, rack of lamb, prime rib. Save the hamburgers and mac and cheese for home.
I have not been on the Grandeur however my sister has a few years ago and loved it.