The generation today is indeed very different as the access in gadgets are quite easy. Hence, parents should be responsible enough on how to manage their kids when it comes to access of these gadgets. As you can't monitor them 24/7, you should still the discipline as to when they can have access and when to use it as well as the sites that they need to avoid.
Parents are the best tutoring materials for underage, children are more responsive to physical prevention than online limitations. Children are more curious, with the little time they have to access the internet can be used to do lots of things they didn't get the chance to do freely. It has to involve different method of prevention both restrictions and impacting discipline even in your absence, the only problem is that children knows various ways to go round any restriction you place them, it will be hard trusting just that process.