The boy gave parents and kindergarten staff at College Road Kindergarten a fright on August 27 when he went missing after being inadvertently signed out with another family.

His mother, who asked to remain anonymous, arrived to pick up her son following the morning session only to find the staff could not locate him.

"I arrived a few minutes late to pick him up, but he was nowhere to be seen, which gave me a terrible fright.

"When the staff checked the sign-out register, another parent had accidentally signed on the wrong line. I went to call triple-0 , and just at that moment a parent walked in carrying him," she said.

The parent was standing with a group of parents chatting at the gate, when he spotted the boy near a reversing car and quickly ran over to pick him up. He had followed his friend out of the building, but went unnoticed in the crowd of parents.

"He likes cars, so I'm not surprised he wandered off obliviously while the parents were chin-wagging," the mother said.

She urged parents and staff to be more "vigilant" when signing children out. Wyndham Council and the Department of Education and Early Childhood Development are investigating the matter.

In a statement issued, the council said, "a thorough investigation of how the event occurred and how future incidences can be avoided in the future is currently under way."

The kindergarten has already changed the procedure for signing children in and out, requiring parents to line up to gather children one at a time.

A security procedure used by privately operated three-plus activity group Aero Tots involves one staff member being stationed at the main gate during pick-up and drop-off times. Another staff member monitors each child and parent as they sign out, while a third sits with children whose parents have not yet arrived.

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