Parents had told investigators their children often seemed groggy after leaving the day care. The charges are the most serious that can be applied, Deters said.
Hartley was the director and Scott was the lead infant teacher at Covenant Apostolic Church Day Care in the Cincinnati suburb of Springfield Township, the prosecutor said. They were fired from the day care after the allegations surfaced in December.
It wasn't clear whether Hartley and Scott had attorneys. There were no phone listings for the women in Cincinnati or Cleves, and a message seeking comment was left at the church.
A co-worker notified police in December that Hartley and Scott gave the children melatonin in candy.
"I understand how upset the parents of these children must be," Deters said in his statement. "Day care workers are responsible for a very valuable commodity and must be held to a high standard."
Melatonin is a naturally occurring hormone that helps control sleeping and waking cycles. Possible side effects of the supplement form include dizziness, abdominal discomfort, headaches, confusion, sleepwalking and nightmares, according to a Mayo Clinic web site.
The site also says that long-term effects are not known and that it may not be safe for anyone younger than age 20.