Unicef said on Tuesday that 27 children died and 10 were injured in the bombing of St Sebastian’s Church in Negombo.
It said 13 children died in blasts in Batticaloa and 15 were injured.
Twenty children have also been taken to hospital in Colombo.
Unicef also says many children lost one or both parents in the attacks and would need psychological treatment.
More than 320 people were killed and 500 injured in the bombings.