Did you have the image copyrighted yet? If not, I believe that you must do so within 30 days of publication to pursue legal action. Any newspaper should know better, however not knowing what was said between the parent and the publication kind of complicates the issue. If the image was copyrighted, I would contact the paper and discuss payment. If they balk, I would sue them. Even though it is your image, and is considered copyrighted when created, It's hard to win a suit without the image being formally copyrighted at the Library of Congress. Check out this brief intro to copyright
here. It's a lot easier to negotiate knowing that you can win in small claims court if they don't want to pay you. Just my opinion.