GWT,
I'm not a lawyer, and I don't even play one on TV.
The following is my understanding of the issue. Frankly, if this really bothers you, get a lawyer in your area to spell it out in writing what your real risks are.
What's the verbage of the User Agreement on the site where you cam? If it specifically states no one under 18 and that users may be exposed to images that offend them, then you are somewhat covered.
As long as you cam in a designated "Adult" area where users have been warned that nudity may be viewed, and as long as you break contact upon learning the person you are talking to is a minor, you are covering your ass, so to speak.
Those that get in trouble are those who upon learning they are speaking with a minor, continue to engage them on a sexual level. Yes, there are a lot of people posing as youngsters on the net and they are purposely trolling for perps. Since there have been several successful convictions of people who have propositioned adults posing as minors, more people have gotten into the act.
This whole entrapment issue alone deserves a thread all its own. But suffice to say, what you are doing is good. Even better would be a statement to them as you sign off basically stating that you don't engage with minors, they have no business being where they are and you are reporting them to the governing body of the site. If nothing else, you are helping keep the site available for your fun as it is intended.