Littering

I have new neighbors who moved into a house around the corner from me.  I admit parking is scarce sometimes, especially with the winter parking rules.  So these people park across the street from me, even though I live on a private way.  No problem.Well ever since they have moved in and parked there I find trash all around their cars.  Everyday I'm out there picking it up and trying to improve the neighborhood.  Seems like a losing battle most of the time.Last month I was outside picking up trash, I saw one of them and asked him not to litter, because I was tired of picking up after him.  He said to me "Who told you to pick up the trash?"  I explained to him that we all live in the area and try to keep it as nice as possible.The other night I heard them outside and I was in my front room.  So I looked out the window and saw their little girl, about 8 years old, get out of the car and just threw some papers on the ground.  So I went outside and confronted the mother and told her to tell her daughter we don't throw trash on the ground.  She said she did not see her daughter throw anything but she was sorry and took the trash from me.  A lot of good that did.  The next morning I went out and there was the same trash the mother took from me right on my front steps.I don't know what to do.  Don't we have littering laws in Medford?  But I guess they wouldn't be enforced anyway.  Is it a cultural thing and these people don't realize you don't do these things?  Any suggestions other than just pick up after them and hope they move in a year.