Emergency crews in Halton Region responded to a chlorine leak on Tuesday afternoon at a public pool in Burlington.
Calls for help came in around 2:00pm from the Lasalle Park Wading Pool & Splash Pad near the waterfront along Hamilton Harbour.
A dozen children between the ages of 4 and 7 were treated by paramedics.
6 of them were taken to the hospital to be checked over, as a precaution.
Halton Regional Police believe an equipment malfunction is the possible cause.
City of Burlington officials were called in to diagnose the problem.