My current fort is a try at a generational fort. One of the interesting things is even though the children have assigned beds, they often sleep in the parents bed.
Even the ones that have grown into adults still follow the mother around and regularly sleep with the parents, even after the economy started and after they are paying rent on their own rooms.
I once saw the father, mother, 2 babies, 9 children, and 3 grown children all in the bed together. Thats 16 dwarves in 1 bed.
I've also seen some odd things with "friends" sleeping together. They all become friends at the parties growing up, then they sleep in the same bed. All the forts children seem to have become friends with the bookkeeper, and they often run to sleep in his bed and vice versa. They don't do it on such a large scale, however. It's usually only 2 or sometimes 3 to a bed.
I also have dwarves piling up on the barracks bed. Even though they have their own room, they seem to enjoy piling up 4 or 5 of them on the single barracks bed. Children and soldiers and farmers alike. The soldiers are even set to sleep in room, so its not like I told them to sleep in the barracks. It's not like theres a bed shortage, I have 1 room for everyone, including the babies yet to become children, and extra beds around for good measure.