InternetSafety
Every child and adolescent should be taught internet safety (and probably all adults, too). The internet is not a safe place. For example, I'm middle-aged and terrifically tech-savvy and the internet is not entirely safe me, either.
To do with sex education there are two main dangers on the internet: There are literally millions of predators on the internet, and there are literally millions of pornographic websites on the internet.
Online sexual predators
The predators know what they are doing. They go where the children and adolescents are. Children and teens are usually complimented by attention from older people, but predators also lie about their ages, too. There is no way to know for sure who someone is on the internet. Predators go where the children are, like Roblox and Habbo Hotel and Stardoll, and to the lawless parts of the internet, like IRC. Predators are very good at getting relationships with children and getting them to do things. They've had lots of practice.
Sexual predators can try to have cybersex with children/adolescents, ask for pictures or videos, or say they already have compromising photos and blackmail the child/adolescent for more photos or for money. Sometimes they get the child to do some disgusting thing on video, and then threaten to release it unless the child or adolescent does more and more really bad things. They can arrange to meet children and adolescents and do sexual things with them, or downright rape or sexually abuse them.
Online pornography
And there are millions of pornographic websites, perhaps tens or even hundreds of millions. Perhaps they vary in nastiness but they're all bad and totally inappropriate. Don't look at porn. Internet porn is addictive?. It causes people, mostly boys and men but definitely also girls and women, to look at more and more and weirder and weirder stuff. People can be addicted for years and end up looking at the weirdest stuff, stuff they'd swore they'd never look at, stuff that'd normally make them throw up.
Then there's the loss of sexual purity from pornography, and the psychological impact of seeing all kinds of perverse and wrong sex acts in the early ages of childhood and adolescence. Adolescents are curious about sex (and they should be, it's an important part of life), and their brains are at the height of neuroplasticity. This makes them easily addicted to internet porn. Children, even pre-teens, are often starting conversations with each other about "What kind of porn do you like?"
Advice for safety
Parents, I would advise you the following. For children, have the child sit on your lap while you use the internet, and check the URL of everything they click on. Do not allow the use of the internet unsupervised. Do not even let them use it in the same room without them on your lap. Only let them use it if you are also looking at the screen constantly with them. For adolescents you need to speak to them about predators, online pornography, and other internet dangers. And then maybe you can let them use the internet in the same room. Do not let them use the internet unsupervised or alone. Do spot checks to make sure they are not on any websites they shouldn't be and they aren't talking to anyone you haven't personally vetted. Don't respect their privacy on the internet, they shouldn't have any.
Children and teenagers, I just said this, but there are millions of predators on the internet and millions of pornographic websites. Do not use the internet unsupervised. Tell a parent, teacher, kids help hotline, or some other trusted adult of you are messaged by a stranger or exposed to sexual material. You probably think you know what you're doing online, but predators know more. They are older and have years of experience. You shouldn't talk to strangers online anymore than in real life. The predator could be anonymous and from another country, so there is little chance of them getting caught. They know this.
Parents should set up pornographic filtering on their devices. One solution is to use Cloudflare's 1.1.1.1 for Families (link below). The free open source operating system Linux Mint comes with MintNanny, for blocking commonly-used inappropriate websites. If I was a parent to a child or adolescent I'd set up both, *in addition to the close supervision mentioned above*. It should make things a little safer.