If you are going to apply under the live-in caregiver program, you can do that after 2 years of working. You will continue to work as a live in caregiver for another 10-11 months until you get your first stage approval. Then you get your open work permit and can apply for any job you want.
It would be faster if you can apply under the skilled worker program, see
http://www.cic.gc.ca/english/immigrate/skilled/index.asp The quota for RN's is filled right now and will not reset until July 1st but if you have at least a 1 year work experience which falls under practical nurse in the last 10 years, you can apply under that category. See
http://www5.hrsdc.gc.ca/NOC/English/NOC/2006/Profile.aspx?val=3&val1=3233 for the job description of a practical nurse.
You would of course include your spouse and children on your PR application.