NEW : Spy swap idea continues with the U.S. Six children of Russian agents have left the U.S. , they say . U.S. and Russia complete spy swap at Moscow airport . Moscow airport the plane landed with 10 Russian agents aboard .
NEW : Spy swap idea originated with the U.S. Six children of Russian agents have left the U.S. , attorneys say . U.S. and Russia complete spy swap at Vienna airport . Moscow airport confirms plane landed with 10 Russian agents aboard .