Parents picked up their children from school after a science experiment explosion at a school in Houston. (Godofredo A. Vasquez/Houston Chronicle via AP)

An outdoor science experiment involving fire at a Texas Presbyterian preschool went terribly wrong Tuesday, injuring 12 students — six of whom were transported to a hospital with burns.

Just before 12:30 p.m., a group of preschoolers from the Yellow School, an early childhood program at Memorial Drive Presbyterian Church in Houston, were gathered outside to watch a teacher change the color of fire using different chemicals, Village Fire Department Chief David Foster told TV station KPRC 2.

The teacher mixed boric acid with methanol, Foster said, and tried to light it on fire. Nothing happened, so the teacher added more alcohol and lit the mixture again. Then there was an explosion.

“I don’t want to make any pre-dispositions that anything went wrong here,” Foster told TV station KHOU. “It was an unfortunate accident.”

Six of the students were transported to the burn unit of Children’s Memorial Hermann Hospital, and the other six were picked up by their parents and taken for treatment elsewhere, reported the Houston Chronicle.

Authorities investigate the scene of a science experiment explosion in Houston. (Godofredo A. Vasquez/Houston Chronicle via AP)

“Fire was changing colors and the last one wasn’t working, so we put it a little bit more, and then it exploded,” Kate Earnest, a 5-year-old who was part of the group that participated in the experiment, told ABC 13. “That’s how the other kids got burned, and they were crying.”

Those children taken to the hospital were in good condition Tuesday afternoon and all but one had been released, a spokeswoman told the Houston Chronicle.

“It’s just scary, you know?” Randy Kenney, whose 3-year-old son was burned during the experiment, told KPRC 2. “We were just coming here to have an end-of-the-year picnic and there was a lot of firetrucks.”

Officials said the children injured were 3- and 4-year-olds.

“This incident will be investigated swiftly and thoroughly, and we will keep the congregation up to date as more facts emerge,” the church said in a statement on its website. “Our primary concern is the health and safety of our children, and the Yellow School asks for your prayers for the injured and their families, as well as staff and students.”

The Texas Department of Family and Protective Services is investigating, reported KPRC 2.

“Child Care Licensing is currently investigating the incident at the Yellow School this afternoon,” the agency said in a statement. “We will interview staff and children and their parents, and make sure the area will be safe for children to return.”

Parents pick up their children from school after the explosion. (Godofredo A. Vasquez/Houston Chronicle via AP)

More from Morning Mix

‘I think we’re in impeachment territory’ says David Gergen, former aide to Nixon and Clinton

Yale dean once championed cultural sensitivity. Then she called people ‘white trash’ on Yelp.

The head of this teardrop-shaped glass can withstand bullets