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.
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.
Maybe not intrinsically, but what I see kids doing handheld computers at restaurants (and sitting in a cart at the grocery store, and getting pushed around town in a stroller, and on public transit, and sitting in their car seats, and at the playground, and at the airport, and on the plane, and at the doctor’s office, and waiting at government offices, ... and I can only assume at home too, though I have a smaller sample of kids I can see at their homes) is playing computer games or watching videos.
I don’t think computer games and videos are inherently evil or anything, but they can be extremely distracting and addictive, and some very small kids are dramatically overexposed to them. For many kids these have crowded out a great deal of social interaction, reading, self-directed free play, ...
Paper and crayons have none of the problems of videos or computer games, in my opinion. Especially if they are being used in a social way with multiple people interacting.
I have found that usually my 3-year-old doesn’t have any problem at restaurants unless the adults are talking to each-other and ignoring him, in which case he gets bored and starts running all around, etc. If we are talking to him, playing little games, drawing with crayons together, reading a book aloud, etc. then he is just fine. YMMV.