What are kids doing on the internet? The answer is simple. The same thing as adults - they communicate, look for information, watch movies and cartoons, listen to music, download applications and at the same time often understand all the subtleties much faster than we do.
Trust your children and discuss their plans and interests with them
Unfortunately the internet is as safe as we think it is. There is a lot of negative content hidden behind beautiful photos or videos. So if you are worried about your kids, install Refog Keylogger https://www.refog.com/keylogger.html on their computer. So you will know about everything that happens.