"Monitoring is one of the best ways to discover what activities your teen is engaging in and be able to proactively address the issues that they will face.

Many parents, however, still hesitate to take that step. To them monitoring feels intrusive, like a breach of their child’s privacy—but there’s an important difference between smartphone monitoring and outright spying that you should keep in mind.
                                                      http://www.teensafe.com/blog/parents-can-monitor-social-media-                                                            cell-phone-tracker-free-guilt/

"You don't need to know the ins and outs of all the apps and sites that are "hot" right now (and frankly, if you did, they wouldn't be trendy anymore). But knowing the basics -- what they are, why they're popular, and what problems can crop up when they're not used responsibly -- can make the difference between a positive and a negative experience for your kid."
https://www.commonsensemedia.org/blog/15-apps-and-websites-kids-are-heading-to-after-facebook#