Two children were left with "burn like" injuries when they came into contact with a pool chemical that had been poured onto playground slides at a park in Massachusetts, fire officials said Monday.

The suspects remain at large and "may have suffered acid burns" themselves, according to a press release from the Longmeadow Fire Department.

Police and fire officials responded to the Bliss Park playground Sunday morning after a report of a "suspicious substance" on the equipment, according to the release.

"I let the kids go play. I did notice that there was liquid kind of collected at the bottom of the slide. I thought -- I just assumed it was rainwater," Ashley Thielen, the mother of the two children who were injured, told CNN affiliate WGGB.

"And then my baby, who's one, just started crying... So that was when I kind of knew that this liquid that they were around was not water," she said.

Investigators later determined that the liquid, which had been poured on three slides, was muriatic acid -- also called hydrochloric acid -- which is used in cleaning and disinfecting swimming pools, according to the CDC.

It had been stored in the pump room in the basement of the park's pool building, the release said.

Officials believe the the suspects broke into the pump room, where the pool chemicals had been "properly stored in a secured area."

"A great deal of effort was employed to enter this space. We suspect that the perpetrators may have suffered acid burns to their hands or arms and their clothing may have indications of being degraded from contact with the acid," the release states.

Thielen said her children's wounds are mostly superficial and that they are okay, but it could have been much worse, she told WGGB.

The playground has been professionally cleaned, but it remains fenced off out of an abundance of caution. All hazardous materials have been removed, and the rest of the park is open, the fire department said.

Evidence was gathered at the playground and pump room by the Massachusetts State Police crime lab, which will perform forensic analysis and fingerprinting, the release said.