Dear nighthawk,
he controls the card. If the children are being denied medical benefits, the mother can take them to get a card as long as they are enrolled in DEERS.
You and the mother can verify the sons eligibilit for DEERS here: http://www.military.com/benefits/tricare/defense-enrollment-eligibility-reporting-system
If he is eligible, he can do to the nearest military ID card facility on a military base and get a new card.
If that fails, then the mother and the son have to file a comlaitn with the nearest Post Inspector General. If that fails, then you have to sue the father in civil court and get the court to order that he provide medical care and authorized military benefits.
http://www.dfas.mil/militarypay/garnishment/fsfact.html
YOUR PAYMENT AND BONUS IF ANY MAY BE TAX DEDUCTIBLE

Edward M. Johnson