Nazila Sharaf, 35, and Lida Sharaf, 33, face three counts each of felony child abuse and neglect.
The children affected are all under a year old.
Police say they uncovered evidence of dangerous swaddling methods at Universal Preschool, formerly known as "Sunnyside Infant and Preschool" in Livermore. Officials say this includes children bound so tightly they couldn't move or breathe properly.
The women are being held in the Alameda County jail.