I have Lake View manor and tried to adopt Lucia, but it doesn't work.

I have a child's bed and a child's chest and the dresser next to the child's bed, as stated in the Uesp page on adopting. But when I talk to Lucia about adopting her I only get the option saying "I own a house but I don't have a room for you".

Is there something more that I need to build / do in order to adopt a child?