You know the story of Little Red Riding Hood, right? The Big Bad Wolf didn't show up growling. He put on Grandma's cap, lay down in bed, and spoke in a really thin little voice to trick Little Red. His mouth said "come here, little granddaughter," but his heart wanted to do something bad!
The Bible says there are people like that in real life too. People who pretend to be friends (they say sweet things), but inside they're jealous or want to cause trouble. That's why we can't trust just any stranger simply because they smiled or offered candy. We have to have Jesus's "Detective Eyes" and always ask mom and dad before trusting someone!