Believing they'd found something special at the local tip, the teenagers picked up the small bottles and later took them to class.
"Thinking they'd do show and tell with the mercury, I think," Paroo Shire Council Mayor Suzette Beresford told AAP.
"They were high school kids who probably shouldn't have been at the dump rummaging."
Instead of an impromptu science display, the discovery has led to Cunnamulla State School, a BP service station, the hospital waiting room, seven private homes, a council depot and the town's refuse tip being cordoned off while authorities race to contain any contamination.
Some families have been moved into an evacuation centre while emergency crews assess whether their homes are safe.
The mercury scare has effectively frozen daily life in Cunnamulla, a town of about 1000 people some eight hours' drive west of Brisbane.
The state school, which has about 130 students, has been shut since Monday.
Authorities believe the mercury may be linked to the illegal dumping of medical waste, but they can't confirm that the dumping was deliberate.
"Whether the people knew there was mercury in whatever they dumped … that's something we really don't know much about at this stage," Ms Beresford said.
The children had been checked and cleared by health staff, she said.
"The children were sent to the hospital, and they were cleared and good to go," Ms Beresford added.
"Nobody's sick, everybody's right. We've now got the QFES people there, the specialist HAZMAT people, and they're going through remediating the sites until we get the all clear."
Queensland Fire and Emergency Services crews are conducting atmospheric monitoring and site testing across the town and say decontamination could take at least two days, with more locations possibly being added as the investigation continues.
