Hi! I've been on 3 cruises and about to go on my fourth this December. I've been in a room with window and to what I like to refer as the "closet" rooms....
To answer your questions......I think that a stateroom of any size would be fine for a family of 3. You spend very little time in your room, especially if it doesn't have a window. There is one very crucial item you NEED to pack when sleeping in a "closet" room....a NIGHTLIGHT! We read about that on a chat log before we went on our first cruise. My husband is **** when it comes to having EVERYTHING, especially the just in case stuff. Anyways....the night light was the BEST thing we could have EVER brought. When you are in a room without window.....you can't see your hand in front of your face when you turn the lights off. Also....bring a power strip. That was another great tip we found. You are limited to like 2 outlets in your entire room! The power strip will more than triple what you have in your room.
Last.....I would book my room on the highest floor I could. I found that I enjoyed being higher up....I like to walk off my meals and take the stairs, but that is just my personal preference.
I hope you enjoy your cruise!