You could let her know that if she insists on bringing kids to kh then you will be bringing kids every other weekend to various faiths of the world. One week will be Catholic, Temple, Hindu, Protestant and so forth....
Do not trust a jw to adhere to any agreement unless it is stipulated by a court of law. In order for a court to recognize that the jw's are in fact harmful to children you will need a good attorney and a child psychologist and possibly a cult expert. This is no joke. Many on this board have lost their children to the borg by trying to be a nice ex spouse and not make things more difficult. Tear that bandaid off and protect your precious child/children now. It's your job as a parent.