An elderly man has been arrested on suspicion of administering poison after several children became ill at a summer camp in England, police said.

Following an initial report from a third party on Sunday, officers and paramedics were dispatched to the camp in Stathern village, Leicestershire, central England, where they evaluated the children.

Eight children were transported to the hospital. They have all since been released, and their parents and guardians have been informed, according to a statement from Leicestershire Police.

The police force has referred itself to the Independent Office for Police Conduct (IOPC) regarding the “circumstances of the initial police response” to the event.

An IOPC spokesperson informed CNN: “Our assessment team has reviewed all available evidence and decided that the matter warrants an independent investigation by the IOPC.”

“The investigation will assess whether there were any violations of professional conduct—specifically a failure in performing duties and responsibilities—that led to a delay in Leicestershire Police’s response to what was subsequently deemed a critical incident.”