After buying the upgrade from Bits and Pieces in Solitude, you can set up the back room for your followers.
Using this option excludes the Children's Room!
You'll get three beds for follower's with a comfy room with a bar and an armory.
Followers need a mod like My Home Is Your Home or have the ability to move in on their own (for mod added followers) in order to accept the place as a home. Not all followers are capable of moving in.