I am a bit confused by the api for entity parents and what i am seeing from entities created by czml. Entity.parent is defined as an Entity which means that Entity.parent.id ought to be the value of the parent id however it ends coming across as ID for some reason using cesiumlanguagewriter. I had to change my jsni wrapper for Entity to return this.id === undefined ? this.ID : this.id in order to get the expected behavior.