A dozen children swimming at a birthday party at a Mississippi YMCA had to be hospitalized Sunday after pool equipment apparently malfunctioned and left uncirculated chlorine fumes in the air.

WLBT-TV reported that Flowood police received a call at approximately 2:30 p.m. Sunday and the caller said the children were choking at the Flowood YMCA.

Police said apparently the pool’s equipment malfunctioned and was not properly circulating water when chlorine was dumped into the pool.

The children were transported to Children’s of Mississippi hospital.