Bad experience in the internet

A bad experience I had on the internet was that I entered a room of videochat that had as a subject "kids videogame", and when I entered the room a bunch of guys were naked in front of their computers and they were looking for children. My parents could have prevented me from these kinds of sites putting a firewall or supervising what I was doing so I would not have seen that. They could also have taught me that many sites in the internet are full of pedophiles and people that want to harm you and take advantage of your innocence as a child.

Criminal activity

If your kid gives too much personal information such as address, phone number, name of his/her parents, where do they work; the kid may be putting him/herself in trouble as well as you and your loved ones. If this information falls in wrong hands such as a criminal's you are in potential danger. I would recommend parents to tell their kids to not give anyone personal information and be careful who they interact with and I would supervise whatever they are using.
https://thedmonline.com/copy-chief-draft-cyber-crime/

Cyberbullying

This is a threat to your kid. Some other kids with access to a computer and an internet connection may spread rumors and bad stuff about your kid. This might potentially lead to suicides, depression, bad performance at school, beatings. I would highly recommend parents to supervise whatever their kids do in the web because they may be or putting someone else in danger.
http://abcnews.go.com/GMA/teenagers-gma-inside-world-cyberbullying/story?id=38133262

Viruses

http://www.cnbc.com/2016/03/28/fbi-probing-computer-virus-at-medstar-hospital-chain.html
Parents should be afraid of these infected files their kids could potentially download to their computers leaving them exposed to personal information and identity theft, messed up computers and exposing them to inappropriate materials such as music, videos or pictures they might not be ready for.