A newspaper delivery driver found Max McGrath outside the supermarket in Somerfield, The Times of London reported. The store was closed, and young Max was looking wistfully through the window.
While the boy's timing was bad, he had come prepared with money and a front-door key to his home, although he left the door open behind him.
"I have a child about the same age and it is terrifying to think what an adventurous youngster can get up to," said James Brown, who found the youngster. "He was fine, but it must have been such a shock for his family."
Brown drove Max home and then called police when he could not rouse his parents.
"I'm still shaking from shock after all this," said Max's mother, Amy McGrath. "I would like to thank Mr. Brown from the bottom of my heart."