I have two children, a boy and a girl, both 16, turning 17 in a few months. They have always been close since they were young and still are. I never paid attention and though it was a good thing until I caught them giving each other a kiss on the lips! They told me it was just a brother/sister thing, and nothing to worry about. Plus, my daughter would often stay in her brother's room a lot and lock the door and whenever I would knock on the door they take a long time to unlock the door to let me see they are studying. But if they are just studying, why lock the door? Another time was when I saw a bite mark on my daughter's neck, but she doesn't have a boyfriend, and doesn't go out that often, neither that my son. I tried asking them if they are sleeping together but they always tell me no. Am I being too paranoid? Or is something going on between the two? I'm just scared and I grew up as an only child so I don't know if this is normal... Please help me. I don't know what to do. They are good kids, they are doing good in school and don't go out partying. I just want to help them.