The children's lives have been turned upside down, and the unsettledness is reflected in their upset. All you can do at their ages is provide as much stability and affection and support as you can. As their mother resumes more normal appearance and functioning, they too will re-achieve the stability they formerly displayed.
Try to avoid, if you can, many comings and goings in their lives, and try to limit the number of people who are caring for them. The fewer transitions right now the better.