I adopted two children with the Hearthfire expansion: one was Lucia (from Whiterun) and the other was Samuel from the Honorhall Orphanage. Strangely, Samuel sleeps in his bed normally every night, but Lucia just stands by her bed, even if I tell her it's time for bed. Are all the children that don't come from the orphanage (that came with the DLC) bugged in some way. I think I read that several of the others (the flower girl and the mine worker boy) get an error where they can't carry anymore stuff.