Teach your children that if they see anyone doing something that doesn't seem right to tell you the parents, a teacher, or another trusted adult.  Some examples are: 

• a stranger hanging around the park or school playground.
• someone unknown offering rides to or from school.
• a stranger offering gifts or treats.
• a stranger asking a child to come with them to help in locating a "lost" dog or cat.
• someone giving away or selling drugs 
• a bigger kid bullying or threatening younger children.

If you become aware of something that you think may threaten yours or other children notify authorities by calling 911