I used this last year with my fifth graders. Students are asked what they think cyber bullying is, and whether it hurts someone physically, emotionally, or psychologically. Students discuss why digital bullying is so much easier than hurting someone face-to-face. Students also read an article demonstrating the consequences of cyber bullying in the real world.
I suggest showing an attention-grabbing video to start the lesson and conversation about cyber bullying. I really liked this one: https://www.youtube.com/watch?v=vmQ8nM7b6XQ
or this one
https://www.youtube.com/watch?v=FYVvE4tr2BI (except the last bit/religious tones may not be appropriate for your school)