The Parent and The Protector

So when should you be concerned about a adult or even a child and their intentions with a child? What is appropriate conversation to have in front of a child and what is appropriate to say to a child? I bring this up because I found out that a man had said something to his niece, who did not get the concept of what was said due to her age. It was a heavily suggestive, sexual and above all else inappropriate comment. It was a comment you would say in the privacy of your own home between two full grown adults who were sexually involved. My niece was there but did not hear the conversation just was told was said. She also didn't get what was being the content of what was being said.
Needless to say because they thought it was a funny saying it was posted on my nieces fb wall as an inside joke by her friend who's house she was staying. Their was no question these two girls knew not what they were posting, which has been removed now. Her mother checks her page and I check her page it's almost a tag team to make sure nothing is missed. Its hard being a parent with having more than one kid and especially three girls going through emotional and physical changes.
So what happens because in this case there is no control or not much knowledge of the situation, you warn. You make sure to let them know the person is not safe, stay away. Don't be alone or near them. If there were more of a substantial evidence and your daughter was the one involved or son as well, more steps should be taken.
Protect your children. Make sure they can come to you with questions and about uncomfortable situations. Also find time for them, have a time set aside each week for ice cream or lunch, when you can unwind and talk. It might take sometime but they will warm up. Remember your still an adult and the parent your not their friend, yes you can be their friend but again you are their parent. I have seen to many parent try to be cool for their kids so they will like them, they forget to be their parent as well. It's not a bad thing either a parent is a protector. Whether it be a no or a hug it's the parent being the protector.