I don’t mean that every kid who is sitting on the subway with an iPad also spends every moment at home doing the same.
But some of them unfortunately do spend lots of time at home glued to screens. I have multiple friends whose older kids have serious problems with TV, video game, social media, etc. habits, which start crowding out many other activities, with the parents not really knowing what to do about it because they don’t want to have a fight every day.
And some young kids who might not be on their video / game machine at home are doing it a lot in contexts where kids would have in the past either been engaged with the world or entertaining themselves. There is a vast difference between a 3-year-old riding around in a stroller looking at a smartphone vs. a 3-year-old walking around on their own feet looking at the world and talking to the adults walking with them.
These devices seem fine to break out occasionally when the parent desperately needs a break from demands on their attention. But there are kids using these devices for extended periods every day.
P.S. The same goes for adults: people should trade their smartphones for a book or a conversation with the person next to them or just some daydreaming from time to time.
This is the whole thing. Don't assume that. When my kids are at home they're inventing elaborate games to play with eachother. When we're in public somewhere where they don't want to be, they're doing whatever gets us through peacefully.