Jesse James has been putting his three children to work. Knowing how close his soon-to-be-ex, Sandra Bullock, became to Chandler, 15, Jesse Jr., 12, and Sunny, 6, during their nearly five-year marriage, he's been encouraging them to "let Sandra know how much they miss her," the actress' friend shares, adding that he got them to send her homemade Mother's Day cards. And he isn't above playing on Sandra's maternal fears: "One time, he phoned Sandra and claimed Sunny was running a fever and asked if he should bring the little girl to the doctor," says her close friend, who adds that more than once, Jesse, 41, has had Sunny call Sandra. "Sunny tells her she misses her and she misses Louis" - something that's bound to break Sandra's heart, considering she's known and loved Sunny since she was a baby. According to her friend, Jesse even used the children to get Sandra's support for the Nightline interview, saying that if he can't save his reputation, it could be difficult to support the kids.