im letting a friend drive my car this weekend with her children but I don't want to get sued if something bad happens

If you lend your friend your car and "something bad happens", you will get sued.  You may not lose, but there is no way to avoid getting sued. You can get your friend to enter into a contract agreeing to indemnify you for any damages you suffer if you are sued due to an accident occurring when she is driving your car, and agreeing not to sue you, but that won't stop you from getting sued by a third party, or help you if your friend is unable to pay (it may not stop your friend from suing you either as she likely would claim fraud if you didn't disclose something wrong with the car and that caused the accident).