(NewsNation) — Four daycare workers in New Hampshire have been charged with endangering a child after reportedly sprinkling food at the daycare with melatonin.

Police in Manchester, New Hampshire, said the unlicensed daycare was run by Sally Dreckmann, 52, who is one of the workers arrested. Three employees, Traci Innie, 51, Kaitlin Filardo, 23, and Jessica Foster, 23, have also been arrested.

Unlicensed daycares are allowed under some circumstances in New Hampshire but police have not said if that was the case in this instance. Neighbors said they were unaware a daycare was even being operated out of the house before police investigated.

According to authorities, the workers sprinkled children’s food with melatonin, which has a sedating effect and is used as an over-the-counter sleep aid. Parents were unaware their kids were being given the drug and had not consented to its use.

Melatonin is a hormone naturally produced in the body and also used as a sleep aid, especially for those dealing with issues like delayed sleep phase, insomnia and jet lag. It’s generally considered safe in adults and does not cause dependency like some sleep medications.

However, the Centers for Disease Control and Prevention recently found the number of children who’ve been taken to the emergency room after ingesting adult doses of melatonin has quadrupled over the past ten years.

Because melatonin is a supplement and not a medication, it is not regulated by the Food and Drug Administration, which means it’s difficult to tell if a product actually contains melatonin or if its contaminated with another substance. For that reason, health officials advise against giving melatonin to kids, though child doses of melatonin are sold.

Police began investigating the daycare after a tip from someone inside the facility. All four of the workers arrested are facing 10 counts each of endangering a child.