Police have arrested the mother of a four-year-old girl who unknowingly brought heroin to a daycare centre and started to hand it out to classmates.

The child thought she was giving out candy, according to Delaware State Police. She had the heroin in a backpack her mother had allegedly given her.

Workers at the Hickory Tree Child Care Center in Selbyville alerted police and medical personnel after seeing some of the children with small bags of an unknown substance.

It was tested at the police station and turned out to be heroin.

The mother, Ashley Tull, 30, was charged with drug offences and endangering the welfare of a child.

The backpack contained 249 bags of heroin weighing 3.7g.

Tull, who also has a nine-year-old boy and an 11-year-old girl, is not allowed to contact the children, who are in custody of a relative.

Several children who had come into contact with the bags, which were unopened, were taken to hospital as a precaution.

They were later released.