I'd call the police first. I wouldn't confront him. Why confront? If he's guilty, let the police handle it.
If I made a mistake in identifying him, oops. If I'm in some stranger's face and he's a child molester, he may be ready to kill rather than discuss anything.
I'd call the police. I'd remain in my vehicle. I'd follow the guy at a distance until the police stopped him. Doing so may even allow you to be an anonymous tipster, which may come in handy once scumbag gets out of jail. At that point your own family may be in jeopardy if he knows who you are and where you live. (Even if I have to i.d. myself, I will to put scum like this away.)
I see no value in confronting the guy, whether he's a relative or not. If I have a relative who's a child molester, I'm not going to try to talk him out of this one event (there will certainly be more later). I'd rather let the full force of the law come down on him, and hopefully he will be introduced to Bubba in prison.