I have a sister that works for the state and deals with children 16 and under in roane, morgan, scott, and two other counties that I don't recall. She has told me the procedure for this before, because it is a lot more grey than you think.
If it's a normal child, typical home, then a call to the hot line is perfectly legitimate and virtually the only thing to do. There is no need to reveal your name or anything and you do it there and everything on your end is square (assuming you are not the sole witness or anything).
However, if the child is adopted or a foster kid, things become really tricky legal-wise, especially if the child is nearing age of consent. Reporting it then nearly always will immediately result in the child being taken custody of by the state, no questions asked. The parents (whether found guilty of any crimes or not even accused) will nearly always be blacklisted from adopting or being a foster parent again (even if the child put themselves in the situation without parental knowledge or under the supervision of another adult).
Basically, if it's an adopted/foster kid, you better make damn sure its true, because your just gonna cause even more upheaval in their life than is already there. And if it ends out being not true, there's a good chance you just cost them a decent home.
And I won't even get started on when 16-17 year old foster kids abuse the fact they are almost legal...