As has been noted the dress code has been relaxed a great deal for the main dining room, even on "cruise elegant" nights. For children of those ages causal shirts (non-T's) will be fine, along with pants, or non-cut off shorts. So no need to worry.
I sorta doubt with you being from Newfoundland you'll want to eat a lot of fish on the cruise. Just in case though, the Glory is one of the Carnival ships with a Fish n'Chips outlet in the Casual Lido buffet restaurant. It's usually easy to get a table as most people don't realize it's there as it is one deck up within the restaurant. Even if you get your food from the regular buffet, or another specialty outlet, it is a great place to sit and eat.
I would go to the Main Dining Room though for dinner!
Hi Kim, welcome to Cruise-Chat. For packing I'd suggest taking a couple of pairs of dress pants with different tops. For the men, polo shirts or a nice Hawaiian shirt on casual nights will do fine. Formal nights aren't like they used to be. I really miss that, but I guess it's the way it's going to be. Take a pair of shoes that can match everything. For example, I take a pair of black dress shoes, a pair of water shoes, and a pair of tennis shoes.
Be sure to try the chocolate melting cake, it is so yummy! Best wishes for a fantastic cruise and once again, welcome aboard!