How Many Nannies Does OctoMom Need?

3/25/2009 4:00 PM PDT

TMZ has learned 18 different nannies from the Merry Poppins to Order nanny agency have been looking after Nadya Suleman's family for the last two years -- before, during, and after the whole Angels in Waiting fiasco.

We're told the army of nannies work in 4-5 person shifts ... which could last up to 12 hours.

The nannies are each trained by Kaiser Permanente nurses -- and we're told Nadya pays for the services out of her own pocket ...

... probably with the allowance she got from Dr. Phil.