Good luck getting a lawyer to take your case. If it was a man with a convicted record who had a history of comitting sexual offenses it would have been totally different. I've studied cases like this and as long as the store can prove that the lady's intent was merely to check if the boys stole anything you are pretty much out of luck. I'm probably going to get flamed for this but personally, I don't have any sympathy for people who sue frivolously. Our court system is already flooded with too many bugus cases in which the plaintiffs only interest is making money.
So I ask you this: Using your own common sense and fair judgement, what did you believe the lady's intention was ? Was it sexual or was it to simply to check if they stole anything. Did the boy's experience any "emotional damages" after this incident happened (keep in mind that this is not rape). If I were you I would try to answer these questions before taking any sort of legal action.