Wikia

Ghost
	<img alt="209-Ghost children" src="data:image/gif;base64,R0lGODlhAQABAIABAAAAAP///yH5BAEAAAEALAAAAAABAAEAQAICTAEAOw%3D%3D" width="300" height="186" data-image-name="209-Ghost children.png" data-image-key="209-Ghost_children.png" data-src="http://images1.wikia.nocookie.net/__cb20121027202410/grimm/images/thumb/7/77/209-Ghost_children.png/300px-209-Ghost_children.png" class="lzy lzyPlcHld" onload="if(typeof ImgLzy=="object"){ImgLzy.load(this)}" /><noscript><img alt="209-Ghost children" src="http://images1.wikia.nocookie.net/__cb20121027202410/grimm/images/thumb/7/77/209-Ghost_children.png/300px-209-Ghost_children.png" width="300" height="186" data-image-name="209-Ghost children.png" data-image-key="209-Ghost_children.png" />
Notables	The Woman; The Woman's daughter; The Woman's 1st son; The Woman's 2nd son
Seen In	"La Llorona"

Not much is known so far about the ghosts. The Woman is listed quite a lot in the Grimm Diaries, but none of the past Grimms could figure out what she was. It is clear however that ghosts are not a type of Wesen.