The internet in it's heyday, when it was a genuinely thrilling place to find information, and quite a lot of weirdness, and before it was swamped by corporate interests.
I remember starting out with gopher and a paper print out of 'The big dummies guide to the internet' which was a directory of almost every gopher and ftp site (pre web) along with a description of what you'd find there. Then the web came along and things got really good for a while. Once big corporations got involved it all went down hill.
Setting up your computer before you go to bed to download a demo for a game that's... 20 MB large! Waking up in the morning to inevitably discover the download failed part way through.
Not all, but most don't seem to have adventures. When I was a kid I'd go off into the woods and build a den or climb a tree, we once spent a whole week trying to dam a stream, god knows why. None of my friends kids go anywhere by themselves, a lot of them do 'forest school' where they'll be taken by adults to a sanitised woodland and taught how to build a teepee with pre cut wood, and it's just not the same thing.
Waking up early to catch your cartoons. Or as an adult, having to be at the tv at 7 to watch the new episode. Everything will be streamed, thats fine i guess you wont have to worry about missing it. But it takes away the urgency to keep up.
I cannot reply to a previous comment, due to it not federating here, but the children of 2020s will literally be online from day one!
There are countless parents that are posting pictures of their newborns on social media, on Instagram or Facebook, straight to a server in California, so imagine that every single person whose parents are like oh, I don't care about privacy, I got nothing to hide bro will have at least one photo there.
And it's not only that. They'll just never get to experience how life goes with no computer in sight, with no smartphones, not even cellphones at all. No computer, and more importantly, no internet, just cartoons on TV such as Life with Louie or Courage the Cowardly Dog or the Looney Tunes series. And even more importantly, no social media. None at all. Nothing to distract you from actually living.
Carrying over heaps of computer equipment (including the mega CRTs before their demise) to your friends house for an all night LAN party that you guys had been prepping for. Then having a blast while parents look at you funny for being into computers.
Oh, and seeing a new BBS at a bus stop that you'd need to go dial into and check out.
Being able to chalk off the often embarrassing or cruel lessons of childhood as something personal, rather than something someone saved in video, to hound you with for the rest of your life.
Not being in constant contact with everyone you know, and not having a neverending stream of notifications assaulting you via your phone.
When you got to see relatives who lived far away, you talked about what had been going on in their life because you probably had no idea.
You read, listened to, or watched the news when you wanted to, unless someone you know told you sooner.
If you had to wait somewhere without a book or magazine, you just sat there with your thoughts. During childhood, you learned how to be bored and practice imagining things.
I wouldn't use "never get to experience" but i would say it's much harder to have that real sense of community that we easily found in the 90s, early 2000s, etc.
People are more connected to others but still more isolated from others. We were less connected to other people back then so people made a real effort to come up with fun activities and bond together. For kids, it's the lack of just playing outside in the neighbourhood with friends. For adults, it's the lack of third places and community/religious events.
Snow days. Instead it's now "pull out your laptops to get on zoom. I once was off an entire week or so bc of a massive snowstorm. Downside, the sewer line underneath our apartment burst and we couldn't stay home that entire week.
Living off the grid. A world where AI and data collection wasn't so massive that even not participating in anything they will have a full profile of you. Data will become compromised until everything leaks out everywhere. When abusive powers will mathematically make future decisions for you, e. g. a. negative personality-health profile which makes a college dropout almost certain and therefore deny you the choice. People think in absolutes and not even partial success is viable. Just like now big corporations have such narrow application profiles that every human not built in a genetic factory is not worth it. I think the world becomes rapidly more hostile to neurodivergence. And all will suffer from it, because thinking diversity is key.
Lead poisoning. I know, I know, there are a ton of other hazards we're exposing ourselves to. We will have our reckoning with things like plastic, but at least lead is something we're aware of and dealing with.
Along those same lines, ozone layer destroying products.
My previous answer to this question was about buying a phone instead of renting from the phone company. I realized that something today's children may never experience is the government actually enforcing antitrust law, and in the bigger picture, the feeling of trust that the government is there to look out for us and will do the right thing.
(Yeah, that trust was sometimes misplaced, but it existed. We also used to believe that the violators of that trust would be held accountable.)
Tying up the landline phone with their dialup modem.
Polio... well they might actually, depending on how anti-science their parents are and if they live in one last two pockets of it, Pakistan and Afgjanistan.
Competent search results, where you could plug in absolute nonsense and it would understand based on context clues. Now it's a braindead AI that decides what it wants to see for you, and if you want to search for an exact thing adding more keywords makes it less likely to find it.