Malicious Neighbors

I have had some trouble with one of my neighbors since moving into this neighborhood a little over a year ago.
It all started out with a 14 yr. old girl (last year) slapping my 13 year old son in the face because they were arguing over a basketball. The girl left a red indented hand print on my sons face so I walk to the girls house and as I am walking up into the yard the mother is already outside and her daughter is screaming at her that she will not apologize. The mother defends her daughter right off the bat and asks me what my son did to her. I inform her that they were arguing and that my sons are not allowed to hit a female so I knew she had not been hit. The mother more or less blows me off because my son never got an apology.
Second incident the girl punches my 10 yr. old son in the back because he was chasing all the little girls in the neighborhood. They were all playing chase and the 14 yr. old girl punches him in the back hard enough to leave a red mark. Once again I am headed to talk to the mother and once again she asks me what my son did first. Never an apology, never any punishment on the girls part. So, I look straight at the girl and told her "this is the second time you have laid a hand on my children and left a mark, if there is a third time I will get you on assault charges" The mother and the girl turned and walked off laughing.
Third incident and it has happened multiple times...
The girl is now 15 and has a learners permit to drive. She has been driving around alone with no adult supervision but as she is doing this and happens to see one or all of my children (son 14, son 11, and daughter 8) on the road in front of the house or on the sidewalk she swerves her car at them like she is trying to run over them, gives them the finger gesture and calls them names. By now I know the mother will not do anything so I contact the police dept. they go to the girls house and talk to her I suppose, I never heard back from them. So now the girls has an adult with her as she is driving but 90% of the tinme the adult is her mother and her mother allows her to do these malicious things and even gives my children the finger gesture herself. The mother also puts her hand up shaping the letter "L" and says losers to my children. This is a grown woman we are talking about. She is in her late thirties early forties.
My children are not the only ones this girl has swerved at or has caused problems with in the neighborhood. There are others.
Is there anything that I can do other than move?
My oldest son will have to go to school with this girl this year and I am sure she will cause alot of problems.

Any advice would be greatly appreciated.

By the way, we live in the stae of Texas.

How about pictures of the "marks" to show to police and maybe rent or borrow a video camera for a week or so so she can be "caught on tape". I'm not being smart, but it would be some proof. You never mentioned if there have ever been witnesses or if any of the other neighbors have called the police about the problems. Have you thought about a restraining order?

No, unfortunately pictures were not taken. The cam-corder is a good idea. I will set it up tonight.
Witnesses only consist of other children. Ages ranging from 6 to 16 years. To my knowledge none of the other neighbors have contacted the police. This is a really nice quiet neighborhood and it seems as though no one wants to get involved or pursue this matter except me. But something has to be done.
I guess I will have to rely on the video camera. Thank you for the idea. I am surprised I haven't thought of it already.

I didn't know if I could get a restraining order.