The youngest, a three-year-old girl, died in hospital in September after rescue services were called to the home where she lived with her mother, 27, and stepfather, 29, in the northwestern town of Conches-en-Ouche.
The girl's entire body -- face, limbs, chest, back and pelvic area -- was covered in bruises at different stages of healing, indicating repeated beatings, and she had been out of school for a week, investigators said at the time. Her six-year-old brother also appeared to have been hit.
The mother and stepfather, both unemployed, were arrested and charged with murder of a minor.
But the judge investigating the case also zeroed in on the fact that no one had reported the ongoing abuse to the police or social services.
In December, police detained the head of the nursery school that the little girl attended as well as the principal of the primary school where her brother was enrolled, local prosecutor Remi Coutin said.
"They were charged with failing to report the mistreatment of a child," he said.
"The nursery school director admitted she had thought she should make a report but didn't do it, notably because she didn't have time," he added.
But "the (primary) school head has denied any responsibility."
Both have been suspended, the regional education authority said.
If found guilty, they could face up to five years in jail and a 75,000-euro ($82,000) fine each.
Teaching unions are outraged.
"They're blaming us for all the ills on Earth," said Thierry Pajot, the secretary-general of the S2de school principal union.
"From now on, as soon as a child has a bruise, we'll report it immediately. We will flood social services."
Guislaine David, a spokeswoman for main primary school teacher union SNUipp-FSU, said school principals did not have enough support.
"There is no nurse, no psychologist, so they end up alone in situations where it's difficult to act," she said.
A friend of the family had seen the girl a few days before her death and tried to call the social services hotline, but the call did not go through because all lines were busy, Coutin said at the time.
The mayor of Conches-en-Ouche in September defended the teachers, and said everybody was in part responsible.
"Why is it that in this town you have people who call me when the neighbor's dog is barking too loud, but I was never told what was happening over there" in this case, he said.