The SANS Securing the Human project has an excellent resource for parents who want to keep their children or teens safe online. This project recognizes that parents may not be as Internet engaged or sophisticated as their children and thus aims to level that playing field a bit while also describing how to have a constructive conversation with children or teens about using the Internet safely, and lastly, how to implement the "safe use" contract parents and kids negotiate.
The Securing the Kids presentation begins by explaining to parents that many Internet safety issues have real world analogs (e.g., bullying, stalking, theft, vandalism, promiscuity) and consequences (e.g., what you share on the Internet can have lasting effects). It continues by suggesting measures to implement to make your children's online experience safer and more positive. The presentation illustates certain measures (content filtering) in some detail, suggesting both free and commercial solutions.
The project is admirably candid that some of these measures (dedicated computer in a public area, filtering and monitoring) may be suitable for younger children but easily bypassed by teens (who will likely have and "manage" their own devices). Parents should not be dismayed by this. My family experience is that lessons about online safety taught early become part of your children's online DNA. My son, daughter, and I all shared a common "computer lab" from the time they were seven and three, respectively, and I'm comfortable with the safety awareness and Internet hygiene they adopted from an early, open online policy, which is as much as a parent can ask for. It was also great fun. At times.
The presentation and handout suggest ways to discuss online safety so that the conversation doesn't become adversarial or critical. Work with your children to set rules they will accept and you can enforce. Informed consent works better with kids than most parents imagine.