How do we legally stop neighbor's child from harassing us?

Question Details:

Our next door neighbor's son rides his bike on our front yard, looks in our windows and throws rocks at our house. His parents don't want us to say anything to him, instead we have to go get them. They say we are harassing the child. They are threatening to call the police when it is their son that is the source of the problem. What can we do to stop this? Important Notice