Many parents of toddlers would probably admit, if guiltily, to enjoying a profound sense of relief when their children finally learn to play on their own.

But those extra minutes in bed can come at a cost. In the case of the parents of Pipi Quinlan, the price of allowing their three-year-old free rein in the house before breakfast could have been £8,000 after she sat down at the computer and purchased a full-size mechanical digger online.

Pipi, from Stanmore Bay, north of Auckland in New Zealand, opened an internet browser and found the TradeMe auction site her mother had logged on to the day before to look for toy excavators.

"The first I knew of it was when I came down and opened up the computer," Pipi's mother, Sarah, told the Rodney Times. "I saw an email from TradeMe saying I had won an auction and another from the seller saying something like 'I think you'll love this digger'."

She added that she had made auction bids on several toy sets and assumed she had bought a toy digger.

"It wasn't until I went back and reread the emails that I saw $20,000 – and got the shock of my life."

She immediately called the auction site and the seller to explain what happened.

TradeMe reimbursed the seller's costs for the auction and the Kobelco digger was relisted. The computer is now kept out of Pipi's reach.