Nazila Sharaf, 35, and Lida Sharaf, 33, are charged with three counts of felony child abuse and child neglect and three counts of misdemeanor child abuse and child neglect.
"I feel very fortunate that we're here talking about it now with all surviving children," Livermore Police Department Officer Steve Goard said.
Universal Pre-School, where the two worked, remains closed after state officials shut it down in March. A 19-year-old whistleblower reported the alleged abuse of children in the Sharafs' care.
After several unannounced visits, police say the uncovered evidence of dangerous and improper "swaddling methods."
"These kids were tied in knots their legs and arms were bound and they were restrained from even moving," Goard said.
Investigators said some children had blankets placed over their faces for naptime.
"It's almost like a boa constrictor on their chest. If they were to roll over on their face, they have no way of rescuing themselves and it could easily cause their death," Goard said.
The sisters are being held at the Alameda County Jail in lieu of bail.