The Napier Primary School in Gillingham, England, said public officials and police are being involved in the investigation into how administrators sent the wrong girl with a man who came to take his granddaughter to a doctor's appointment, Kent Online reported Monday.
The mistake was not noticed until the girl arrived home and gave her parents the medicine she had received from the doctor's visit.
"My daughter's been known to tell a tale or two so I took her to the surgery and the doctor said, 'I saw her this morning with her grandfather,'" the girl's father said. "When your daughter has been walked round town and taken on a bus by a strange man it makes you sick to the stomach. It's every parent's worst nightmare."
Officials said the grandfather, who is in his 70s, did not notice the girl was not his granddaughter, who is the same age and has the same first name.
"The safety and care of all of our children is of the utmost importance to us and we are treating this matter extremely seriously," said Zerina Slade, head teacher at the school.
"As soon as we realized this had occurred, we launched an investigation. This has not only involved speaking to staff to find out how this could have happened, it has also involved reviewing all our procedures in connection with children's safety," Slade said.
Police said they spoke to both families and determined no criminal offense had occurred. Social services has been notified, police said.