The owner of a Manchester, New Hampshire, day care firm and her employees were arrested Thursday and accused of sprinkling melatonin onto children’s food.

Melatonin is a hormone that helps regulate the body’s sleep cycle. When taken as a supplement, it can help people fall asleep, per the National Institutes of Health. And too much of the product can cause vomiting, diarrhea and seizures, especially in youngsters with low tolerance.

Investigation into day care owner Sally Dreckmann, 52, and employees Traci Innie, 51, Kaitlin Filardo, 23, and Jessica Foster, 23, began last November, the Manchester Police Department said in a Facebook post, after detectives were made aware of allegations of unsafe behavior against the in-home day care.

Parents didn’t know about or consent to the alleged use of melatonin, police said. Each suspect has been charged with 10 counts of endangering the welfare of a child.

“It sounded like it was a powder-type substance, maybe pills that were broken up. I don’t know exactly, but it was described as it was sprinkled on the food that the children were being served at lunch,” MPD spokeswoman Heather Hamel told Boston TV station WHDH.

None of the purportedly dosed children required medical treatment, according to Manchester ABC affiliate WMUR-TV.