Ashley Griffiths, from St Ives, was slapped with the hefty four-page bill from Apple on Sunday.
The boy and the girl had purchased virtual pets and clothing for two iPad games to the cost of 979.90 pounds 'The Telegraph' reported.
The extra amount that rose up to as much as 75 pounds, was purchased using a password.
Griffiths said his children knew the password after using the iPad for schoolwork and games.
He suggested app designers should also demand credit card details when making in-app purchases, the report said.
"I mean, who in their right mind is going to pay 75 pounds for a virtual pet?" he said.
Griffiths added the password has now been changed, and the company has since refunded the amount as a goodwill gesture.