Guy Ritchie fears his that his ex-wife Madonna will break their custody agreement and keep the former couple's children in America with her, according to the director's dad. Richie and Madonna finalized their divorce last month, and are said to have decided to share custody of their 8-year-old son Rocco and 3-year-old David Banda, with the kids splitting their time between New York City and London. Madonna's 12-year-old daughter, Lourdes, from a previous relationship, will remain in the U.S. with her mother. The children are currently accompanying Madonna on the Latin American leg of her Sticky and Sweet world tour, while Ritchie works on his new "Sherlock Holmes" movie in Britain. But Ritchie's father, John, admits the star is worried his ex-wife will renege on the custody deal. John Ritchie tells British magazine Closer, "The children are with Madonna at the moment. Our worry is that she won't send them back and Guy hopes she won't keep them."