A Texas preschool teacher has been arrested after four students were exposed to THC on Halloween.

According to a statement released by police in Prosper, Texas, obtained by KXAS-TV, an NBC affiliate out of Forth Worth, Texas, four children in Primrose School of Prosper's toddler classroom received treatment after authorities were alerted to a "medical emergency" at the preschool on Monday afternoon.

Preliminary evidence, say investigators, suggests the children were exposed to THC, the active ingredient found in marijuana.

Primrose School Prosper Texas
The Primrose School in Prosper, Texas Primrose School

In a statement released Tuesday, the school said they called 911 after observing four toddlers "displaying unusual symptoms."

Anisah Burks, 35, a staff member, now faces charges including felony possession of a controlled substance and four counts of injury to a child.

It is unclear how the children were exposed to the THC.

Primrose School confirmed in its statement that Burks had been arrested, adding, "We have every reason to believe, including from the authorities, that this was an isolated incident involving one teacher who was immediately terminated."

The Texas Department of Family Services and the Child Care Licensing Division has since been notified of the incident, police said.