Sucks for us geezers that learned things the other way around though!
Circa 2004, when 25 year olds would probably be migrated out of diapers, smartphones were palm treos and Sony Ericsson K700s. I don't think they would be great distractions for kids, there certainly wouldn't be any endless Spiderman/Elsa YouTube to lock them in.
At least, in my anecdotal experience.
People seem to forget that "smartphones" (in the post-iPhone sense) are barely old enough to drive. The first iPhone came out in 2007, android doesn't drop till the following year, and the first iPad doesn't come out till 2010.
If you were a kid with a video-playing smartphone before about 2012, your parents were pretty damn well off, and likely early adopters too
Meanwhile, the rest of the Palm Pilot UI (all the parts that were actually on the screen instead of below it in the dedicated writing area) looks thoroughly 90s: the basic buttons, drop-down boxes, tabs and dialog box layouts, scrollbars that aren't trying to hide from you. The main UI elements missing from the Palm Pilot that were present in eg. 90s Mac OS or Windows are the free form desktop layout (instead of the smartphone-like app launcher grid), and the persistent on-screen menu bar or taskbar.
The Palm Pilot UI was unquestionably designed around the assumption of higher precision than today's touch-oriented UIs. The stylus was not considered optional. The lack of capacitive touch sensing for gesture recognition meant the UI was much more reliant on precise button taps where today's smartphones would use swipes and other gestures for stuff like scrolling or "back".
To your second paragraph: of course it looks “throughly 90’s”. It was the 90’s. Did an LLM tell you to say this? I have no idea what scroll bars have to do with anything. I can tell you they were a pain to use. That hasn’t changed.
To your third paragraph: the stylus wasn’t optional. They didn’t just “lack” capacitive screens. It didn’t exist yet at scale. This was what Apple brought to the market. You couldn’t really have them if you wanted them. That being said, I used these interfaces while walking, riding in a car, and sitting still. I never had trouble tapping the right thing because the buttons were huge in the UI.
You do bring up a good point about there not really being swipe gestures to go “back”. I don’t use them today, so I’m not as familiar with that type of behavior other than to say it is really annoying when done by accident, usually while picking up the device.