XainAmir: I believe there is a cut-off age for a child needing a live-in caregiver. If your son is under that age, it should work or if he's sick, it's worth a try. You should call CIC and ask them. Their contact info is here:
http://www.cic.gc.ca/english/contacts/index.asp If it doesn't work for you to hire her, you might be able to find an agency/family who will.
Suin: I have never heard anybody hiring their mother as a live-in caregiver but I don't see why you can't, as long as she has the experience or course. I have heard of people hiring relatives before such as a sister or a niece.
In both cases, the relative coming as a live-in caregiver, like any other person coming on a temporary visa, needs to show that they will not overstay their visa. Depending on how difficult the embassy is in your home country, some seem to believe everybody is planning on overstaying, this could be hard, especially if there are no other relatives left in old country anymore.
They do also need the required experience or course. Nurses have been allowed to take live-in caregiver jobs without the experience or course while I've heard of a case of a person who had experience as a teacher of young children being denied.
You can find info on hiring a live-in caregiver here:
http://www.cic.gc.ca/english/work/apply-who-caregiver.asp Information for the caregiver here:
http://www.cic.gc.ca/english/work/caregiver/apply-who.asp A caregiver can either be a nanny for kids or an assistant/companion to a disabled or elderly person.