Seven children under the age of eight have been hospitalized in Virginia after a suspected overdose on Wednesday evening, police say.

Officers in the city of Hopewell were called around 5:30 p.m. to a house at 100 South 16th Street, where they found the children. Four were breathing but unresponsive while three were awake but appeared to be in a lethargic state, reported local TV station WTVR.

The unconscious children were identified as the youngest in the group, aged 1, 2, 3 and 4.

Police think the oldest child, who is 7, gave the others a prescription drug before also taking one. Investigators believe this was a sleeping pill, but the open bottle they found didn't have a label on it, so the product could not be identified immediately.

All seven children were rushed to hospital. Two of the youngest were later transferred to another medical facility in a serious condition.

Police say all the children are expected to recover.

"They are expected to recover, but because they don't know exactly how much of the prescription medication they ingested... they are having a harder time processing and metabolizing [the drug]," Hopewell Police told WRIC.

The investigation is ongoing, but police believe the children had been left unsupervised. According to police's reconstruction of the events leading up to the 911 call, a mother dropped off three of the children to be looked after by a woman living in the house with her own children, WRIC reported.

The woman babysitting the group of children is then thought to have gone to the corner shop to buy groceries.

"They were left unsupervised for a short period of time and one of the kids that have prescription medication got into it and shared with the other children here," Lt. Cheyenne Casale told WTVR.

When the woman returned, she noticed the children's lethargy and then the empty prescription drug bottle on the floor, according to WRIC. She called 911.

After searching the property, officers removed prescription drugs that they believe might be similar to the ones taken by the children.

The incident has also been reported to Child Protective Services.

Casale told WTVR that the police's priority is to "find out who are we going to hold accountable and get these kids in a safe environment—that's our number one goal."

Newsweek has contacted the Hopewell Police Department for comment.

There are currently no sleeping drugs approved for children, but childhood insomnia is sometimes treated with melatonin, herbal remedies or mild sedatives. The effects on children of sleeping pills containing antihistamines, benzodiazepines or other sedatives have not been widely investigated.

Join half a million readers enjoying Newsweek's free newsletters