Police have stepped up their monitoring of registered sex offenders to help keep trick-or-treaters safe this Halloween.

Experts say parents should check the sex offender registry for offenders who live in the neighborhood.

Laura Ahearn, of Parents for Megan's Law, says there are 1,100 registered sex offenders in Suffolk County and 547 in Nassau.

“Children should not go to the door alone,” she says. “We often see parents at the end of the driveway. That's a mistake, because a candy bar can be the very first step in a process for a sexual predator to start grooming a child.”

Police say children should never go out alone on Halloween night. Nassau Police Commissioner Patrick Ryder says kids should trick-or-treat in groups and not go inside strangers’ homes if invited.

Experts also advise parents to put reflective tape on their children's costumes and bags so they can be seen at night.