They don't have to have those. Depending on your definition of "kids", most people on HN I imagine are not giving their kids phones, laptops, or tablets at young ages (maybe less than ~13?). And if they do, I imagine the devices are somewhat locked down and monitored.

I think the more technologically literate a person is, the more wary they are of unfettered access to it for children. Hence, preferring a stationary desktop where use can be supervised.

I agree desktops are best, and they are what my kids started with, but there is a lot of pressure to give kids phones.

For example, where I live, the cheapest (monthly) bus tickets require an app, so kids need a smartphone to get to school (or their parents have to pay a lot more for daily tickets).

There is a lot of social pressure on the kids too. There are lots of activities that have either moved online or are organised online. Lots of ways to get left out.