You certainly can make your feelings known to the court or to the prosecutor. It may or may not make a difference as to what happens. The other parent may speak on behalf of the victims, the children in the car. There is nothing that prevents you from making this contact.
While some people might discount your opinion because of your relationship to the accused, you can certainly make your knowledge of the accused's prior behavior and your concerns about her current behavior known to the prosecutor. You should do this as soon as possible if you want them to take your feelings into consideration. (You might first try calling the prosecutor's office and asking them who is handling the case. This would be faster than writing a letter.) Your concerns are appropriate.
You may certainly contact the prosecuting attorney and express your concerns. However, the issue regarding the children has little to do with the underlying offense and is unllikely to impact the case.