You would not have a small claims case but depending on the wording of the actual order, your husband might have a motion to show cause that he can file against the mother of his child. The issue may be whether or not that clause is actually enforceable. Depending on how it is written and how much your insurance premium is, she may not have to pay a dime. technically you do not have to provide insurance for her son as you are a legal stranger. You are choosing to provide insurance and therefore that could be construed as a gift.