Two of Octomom's former nannies have told officials ... Nadya Suleman allowed one of her children to sexually abuse another child inside the home ... this according to reports.

According to CBS2 in L.A., the 2 nannies have been in contact with Child Protective Services ... and told officials they personally witnessed the abuse.

The nannies do not say Octo personally sexually abused the children -- but according to one of the nannies who spoke with CBS, "(One of the boys) would take (his sibling) away and take her to another area. And he would be touching her."

Read more in TMZ.