A young boy became violently ill after drinking heroin-substitute methadone.

The child became sick and disorientated and a court was told that drinking just 20ml of the fluid could have killed him.

Chelsea Kerrigan, 27, said she was looking after the boy and his brother with her partner Craig Gibson when the children had found the drug.

Perth Sheriff Court was told 38-year-old Gibson had died of a suspected drug overdose since the incident in January.

Kerrigan told the court: "Craig went out with a pram to the bin shed. The [youngest boy] went out behind him. Then the two of them were sitting at the table.

"I saw the bottle at his mouth and said, 'What is he drinking?' I ran over and grabbed it. The other boy said the younger one drank some and he had licked the lid.

"I gave him a drink and that wasn't working. I phoned NHS 24 and they guided me through it. Craig said to tell them it's getting worse."

She continued: "I didn't know how much he took. I was told 20ml could kill a child. I said, 'He's just thrown up and he's disorientated' and she said an ambulance was on its way.

"Craig took the bottle and put it in the kitchen and poured a bit out so they could see the green stuff. I knew he [the child] drank it because he had a bit on his lips."

Kerrigan told the court she was prescribed 70ml of methadone daily and collected three bottles for the weekend on a trip to the chemist on Fridays.

The court heard the substance the boys found was in a bin bag and had no marking on it to suggest it belonged to Kerrigan or her partner.

Kerrigan, of Perth, was alleged to have "wilfully exposed" the children to unnecessary suffering by allowing them to get methadone while they were in her care.

The trial heard how a check of computer equipment found the couple had searched online about children taking methadone nearly an hour before medics were called. Both boys made full recoveries.

Solicitor Paul Ralph, defending, said Kerrigan had no case to answer as the trial heard no evidence to prove the methadone had come from Kerrigan's home.

"The Crown is not able to establish the bottle came from the house," he said. "I fail to see how she has done anything that is criminal."

Sheriff Gillian Wade agreed and acquitted Kerrigan. She said the only evidence of non-supervision of the child was the period he spent at the bin shed with Gibson.

She added: "The child was outside with someone else. Somehow the child came to ingest methadone, that is a known fact.

"How did this accused enable him to have access to the bottle? Is there any evidence of this bottle belonging to Chelsea Kerrigan?"

Gibson had also been charged with wilfully exposing the children to danger by enabling them to have access to a bottle containing a substance believed to be methadone.

The case against him was due to call at Perth Sheriff Court alongside Kerrigan, but the court was told that Gibson had died.