It is a scary thought.
Suddenly their world is very removed from the world you have been controlling, albeit from a distance, over the past few years.
Now they have all sorts of information, pictures and anonymous comment pages at their disposal. How do you monitor what goes on? How do you ensure your child isn't being targeted, victimised or being exposed to things they are not emotionally ready for?
Maybe you don't.
Maybe they should have already learned the tools to cope with all these new experiences that lie ahead, online safety included.
But that doesn't mean we can't worry about it - drastically.
That's why one mum took some serious liberties when it came to monitoring what her teenage children were up to online.
Mum-of-four Shona Sibary revealed on ITV's 'This Morning' that she believes that the more she spies on her children the safer they will be. She says she has often broken into her teenager's phones to check their safety.
She was part of a discussion asking if parents overreacting to their children’s use of social media is causing anxiety in teenagers.
She said: “I have an 18-year-old, 16-year-old and a 14-year-old. The 18-year-old was absolutely pathologically private… it was so difficult to get into her phone and she went completely off the rails as a teenager. I felt her whole life was being ruled by this rectangular device which, by the way, I was paying for. So my view is that you don’t have a right to that level of privacy when I pay for your phone. I have a right to know what’s going on it.”
Other mums disagreed.
Some argued that teens had a right to privacy and that snooping into their phones was akin to reading their private thoughts in their diaries.
Some tweeted their disgust over social media:
She’s teaching her children to be untrusting of people. It’s ridiculous. #thismorning.”
Another commented: “I’d hate that Shona to be my mother. I trusted my kids, I didn’t look at phones I didn’t follow them when they went out either #ThisMorning.”
Where do you stand on this issue?