Toddlers under age 3 make up the largest group of children under the protection of New Jersey's child-welfare system. They are also the most vulnerable for abuse and neglect, and most likely to die from maltreatment, according to a disturbing new report released Tuesday by Advocates for Children.

Most of those who died, about 80 percent, were under age 4, while nearly half were under state oversight, said the report titled "The Littlest Victims: Protecting Babies from Abuse and Neglect." It makes a strong case for more steps to keep children safe.

Nowhere is better supervision needed than in the state's foster care system, which has had a mixed record in handling cases in which children died. A third of the children in foster care are age 3 or younger. They are more likely to remain there longer than older children, the report said.

The state's Department of Children and Families has been under the supervision of a federal judge since 2003. It has been cited for a number of high-profile lapses in oversight, including mishandled cases in which children died. New concerns about the state's child protection system arose last summer after a Camden child was decapitated by his mother before she took her own life.

State protective-services workers had stopped visiting Chevonne Thomas, 34, who had a history of drug abuse and mental illness. She was reunited with her son last April after having lost custody three times. The state was preparing to close the case.

A report issued earlier this month by Department of Children and Families Commissioner Allison Blake concluded that social workers could not have "prevented this child's" death nor could they have known that Thomas was in distress. But the three-page report provided few specifics about the Thomas case that would reassure the public about the welfare of the 53,000 children under state supervision.

The state should act on several recommendations made by Advocates for Children of New Jersey, including mandatory training for anyone who handles cases involving children and toddlers in the child-protection system.

Meanwhile, a recent report on child welfare in Pennsylvania also offered mixed findings. Fewer children in the commonwealth are entering foster care, and fewer of those who do remain in the system for long periods, said the Pennsylvania Partnerships for Children report. Yet Pennsylvania ranks last nationally in its percentage of foster children who land back in the system after reuniting with their families.

Both reports show there is much work to do to protect children.