Oranga Tamariki says it faces an ongoing battle to keep children safe in state care.

It says 103 children in care were harmed in the first three months of the year.

Almost half of those experienced physical harm and 19 were exposed to sexual harm.

Deputy chief executive of voices of children Hoani Lambert told Mike Hosking social work not a science, it's an art.

He says each case bring its own challenges and in some instances they haven't been able to keep children safe from harm.

"The harm tends to come from those not immediately connected to the children. A lot of harm occurs from those who aren't caregivers, parents or staff."