J.S.
it sounds like what i know of night terrors. with my little one, and with my many younger siblings, we found that eating or drinking helped to soothe or awaken them. of course, do this carefully to avoid choking. with my almost two year old, we just stuck a sippy cup of water into her mouth, one that would dribble some when tipped. it usually works great for her. you can try carrying them outside; there is something about the night outdoors that works a sort of magic on many young children. my niece would sometimes snap out of it for daddy, but not mommy. one of my brothers would sob in his sleep when he was older, like 14, and we fed him grapes or something sweet....it just worked for him. i hope you find an answer. i don't think there is ANY harm in holding and rocking or singing. and whether they respond or remember is immaterial; you are giving them love, comfort, and presence when they are sad. i believe their body or spirit senses this and soaks it up.