Am I liable if a child gets hurt on my property in the state of NC?

First off, I live in North Carolina. I have a "rough" family living beside of me and they recently bought their 12 (or 11) year old son a dirt bike. They could really care less about their childrens safety but, they are the type to sue somebody for anything and any reason they can. Even if I put signs up am I still liable if they ride on my property, without my permission, and hurt themselves? If so, what can I do to cover myself? Thanks for any answers!