What to do when husband kidnaps children in Florida.?

I have a friend who is currently in the military, stationed in Washington D.C. She recently told her husband, who has residence in FL, that she wanted a divorce. He has told her that he is no longer in Florida. He will not disclose where he is or where her children are. She has not filed for divorce yet, it's in the works, but how does she take legal action to force him to at the very least disclose the location of her children. He has stated that she could have their daughter but that he was keeping their son. She wants to know what she can do, can she file a kidnapping charge against him even though they are still married? Being that she is in the military, she cannot just leave to go and find them without repercussions of military punishment. Also note that he has called her and threated suicide stating that he is going to kill himself and he is going to tell their children that the reason he is going to kill himself is because of mommy. Thanks for any help you can provide.