When I started playing one of my older characters I got a letter from the steward in Dragonsreach talking about a change in the furnishings for Breezehome. We can now choose between a child's bedroom or the alchemy laboratory. My guess is that in preparation for Hearthfire the alchemy laboratory was bugged while they developed the bedroom option. I haven't tried buying the laboratory so I can't confirm that shows up yet.

No it was just bugged you can give up the alchemy room in several houses for a childs room. Hearthfire simply overrides the bug.