Sir Paul McCartney's grandchildren have recorded their very own version of Beatles hit WHEN I'M SIXTY-FOUR as a 64th birthday gift for him. MARY and STELLA - his children with late wife LINDA - sneaked into the iconic Abbey Road studios in London with their kids ARTHUR, seven, ELLIOT, four and Stella's one year old son MILLER to record the track, with the help of Beatles producer SIR George Martin's son GILES. It will be played to Sir Paul at an intimate family party at his estate in East Sussex, England tonight (18JUN06) - in a bid to cheer him up after his split from wife Heather Mills. A family friend reveals, "Stella and Mary know exactly how down in the dumps Paul has been feeling. The trauma of the break-up and then the shock of finding out more about Heather's past left him shell-shocked and at his most gloomy in years. "But they are determined to put a smile back on his face for his birthday and thought this would be the perfect way. His marriage to Heather is over but they want him to know he still has his family who are utterly devoted to him."