Hi! We stayed in a dormer room in Sago Cay on our honeymoon in 2000. We were in room 5441 and this particular room has a king bed. However, not every dormer has a king. I think most have two queens. We also stayed in a standard (non dormer) room in 2001 in Conch Key. I think the room was 3001...not 100% sure about that. Anyway, the only difference was that the standard room has a daybed. The dormer has a little couch, but it is not as big as the daybed. However, the biggest difference was the ceilings. The dormer room has these vautled ceilings which give the room such a spacious, open feel! I loved it!!!! Now the balcony is small with the dormers and is closed off, so you can't sit and see much. With the standard room, the balcony runs the length of the room and has an open railing and you can sit and see whatever your view is. In the dormer, we had a castle view and sat on our balcony and watched the 4th of July fireworks. (Very awesome!). In our standard room, we were facing the marina, and since we went in December and it was cold, we didn't use the balcony much. The cool thing about both our rooms at the GF was that we could hear the train whistle and the howling of the wolf from the Haunted Mansion. So magical!
So for a family of 3, I would recommend a dormer room, especially if you are getting a garden view and not a lagoon view room. But even if you are getting a lagoon view room and end up with the magical view of the castle, you will not be disappointed with the dormer!
I hope this helped. Have a wonderful trip!!!!!