Prince William spent Father's Day with his and Kate Middleton's two eldest children, 7-year-old Prince George and 6-year-old Princess Charlotte.The trio visited the Sandringham Estate in Norfolk, England, on Sunday, to kick off a local half marathon. George and Charlotte matched in navy shorts, with the young prince wearing a plaid button-down shirt while his sister sported a pastel pink polo sweater. Their proud dad invited his children to kick off the race, as they all counted down in the