If he was a convicted molester, I'd knock on his doors, explain that there have been rumours about him in the neighbourhood, and that I thought that rather than talking behind his back I'd come and speak to him. I'd listen to his explanations, ask him if he himself had been abused etc., generally try and lend a sympathetic ear. I'd tell him that everyone in the community would hope that he will have a happy time and that we hope his stay is fine and 'trouble free'....then I'd leave...oh yeh but before I'd left and still with the same welcoming a social manner I'd say 'Just one last thing...you lay a finger on any of our children' still smiling...not forced 'I'll make sure that before its reported I'll lynch you till you're nearly dead, drag you around the neighbourhood from the back of a car, then gut you in the street, what I like to call 'Hung, Drawn and Quartered' still smiling 'remember you need anything just let me know.'
(P.S. I think I'm going to call this the 'friendly neighbour approach' ©®)