Do I have any rights if I found out my ex wife was killed in an accident?

Unless your parental rights have been terminated, then you are the only parent and have custody of your minor children. You need to look at your divorce decree or separation agreement to determine if you have any financial rights in your ex-wife's estate. As the natural guardian of your children, you should investigate the death of your ex-wife to see if your children need to sue for wrongful death.