An investigation is underway at an elementary school in Texas after preschool teachers allegedly handed out stickers to students that were believed to be sleeping pills.

Lisa Luviano, the mother of a four-year-old student at Northgate Crossing Elementary School in Springs, told ABC news station KTRK-TV that her daughter came home from school with a sticker with a starry design.

“She said, ‘That’s a sleep sticker,’ and I asked her, ‘Where did you get that?'” Luviano told KTRK. “She says, ‘Well, my teacher gives it to me to sleep with.'”

Luviano said after hearing her daughter’s response, “I was literally scared just thinking about what was going on at school.”

According to the National Institutes of Health, Luviano believes the sticker placed on her daughter was melatonin, a hormone that plays a role in sleep.

The day after speaking with her daughter, Luviano said she went to school to report the sticker. She told KTRK she believes her concerns were not immediately addressed.

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“They said they would keep up with us and be there for us,” Luviano said. “Two days later…the teacher is still there.”

ABC News obtained an email in which parents of Northgate Crossing Elementary students said the principal had informed them that the two teachers and two aides involved had been removed from the classroom. The email said the employees have been placed on leave as police investigate the allegations.

“The news that a teacher allegedly administered melatonin to a student is deeply disturbing and completely unacceptable,” the email said. “Under no circumstances should a staff member administer medication to a student without appropriate procedures in place.”

No charges were filed against school employees.

Luviano told KTRK the alleged incident was “unacceptable.”

“We send our children to school knowing that they will be safe here. We trust our teachers,” she said. “For this to happen. This is unacceptable.”