My sister is contantly talking to my children ages 12, 9, and 6 about bringing them to child services to get them taken away from me. I do not want them to go there, but my ex husband uses her for a babysitter. I feel it is emotionlly tramatizing them, they talk to me about it when they come back with me. I am at my witsend with this, I have told her to stop but she then threatens me with other things that are totally ridiculous. She will not willinglly stop this behavior. I have to do something.

Most likely not a protective order, but you can go back to family court and show that your ex by using her is trying to alienate the children against you. Perhaps restict his visits, and ban her from seeing the children