#2 hasn't even arrived yet, so I'm getting slightly ahead of myself, but DH & I were just chatting about this...
We have 3 bedrooms, 2 are fairly big, and the other, while still being a decent size is about half the size.
I had imagined, that once #2 had stopped the waking-in-the-night-due-to-teeth bit, (s)he & DD(2) would both into one of the bigger rooms together, so freeing up the smaller room for clutter stuff like the clothes horses, ironing board & maybe a sofa bed incase anyone is ever brave enough to visit us.
DH on the other hand, doesn't see the point in them sharing - he says, we have three bedrooms, they'll end up in their own rooms when they're older anyway, so why make them share now?
Do your DCs share a room? Would you choose for them to share if you had another room? If your DC are different sexes, at what age do they need to have separate rooms?