No, stop blaming the victim. Especially since we're talking about young kids who don't know any better. You really expect 3 year olds to say "I think I've been spending too much time watching awesomeness on my tablet. I'm going to meditate instead." Bullshit. What world are you living in?
If I sneakily lace your food with cocaine for a month straight, is it your mental or moral failure when you beg me for another bite not even knowing there's drugs in your food? No. It's my fault you got addicted. Same with smartphones. You are correct in that the physical smartphone by itself doesn't cause those issues. It's how you use it that's the issue and so many things about smartphones and the apps/websites people use on them are designed to enhance those addictive properties. We were already rolling down the slippery slope with TV and movies shortening scene lengths, but smartphones and the quest for clicks supercharged that.
Prior to smartphones, most things were physically limited. You have to go buy that addictive food, unwrap it, and make it. All that takes time and effort with a limited resource. TV shows used to be on at specific times and whatever came next was crap. You couldn't binge watch anything. Video tapes required physical effort to swap and FF until you got to the show/movie and you'd have to stand up to do that every 2 hours and rewind the tapes for next time. Tables/phones are completely different. They're carried with you. They always have a net connection. Battery life lasts a full day. There's nothing stopping you from constantly using them except your willpower and every mass marketed thing on them is designed to maximize your attention to that thing. Kids don't have any defense against that. How they're designed to be consumed turns you into type of person you're claiming is inherently flawed. Those people aren't broken, they're optimized towards a poor path. We're dynamic creatures. We adapt to our environment so nearly everyone using these devices will slide down this slippery path unless you specifically know about it and make an effort not to do so. The counter claim to your argument is that when you remove the devices, people slowly regain their attention spans and self control. If they were inherently flawed as you believe, then they wouldn't be able to get better without meds.
Taking away the smartphones won't fix people's BMI or sleep troubles, it won't bring back their executive functions, and it won't force people outside or to be better at socializing. People's screen time will go down as their underlying issues are solved.
Yes it will. Staring at bright lights in the evening lowers your quality of sleep. Using light to control your circadian rhythm is one of the most effective treatments people with circadian rhythm disorders use. This is all well documented. Not constantly context switching will improve executive functions. Not having your attention constantly consumed by the device will lead you to do something else out of boredom, such as going outside and interacting with other people. Reduce someone's screen time and their underlying issues improve. Granted you may have started using your device in a poor manner due escapism or some other issue, but once you start, it's self-reinforcing. That's true for anyone starting for any reason. Without a smartphone the person might turn to another form of escapism, but the other options have more physical limiters on them. Even if the person ends up glued to a PC playing video games, they have to step away from the PC to get food and piss (well, nearly everyone steps away for that). You never have to step away from a phone/tablet (and prescription smart glasses means you'll never have to look away either).
In conclusion, you're blaming the victim to make yourself feel better and stronger than them. You're not. Use your device the same way they use theirs and you'll end up with the same issues. The issue is also way too wide spread and popped up too quickly for it to be some type of genetic issue. You can claim nutrition is an issue and it is (willpower is directly tied to your energy which is tied to your nutrition), but you didn't make that claim. You have to know you have an issue, have a reason to fix yourself, have the knowledge on what to change, and have the willpower to do that in order to fix your issues. Kids don't have any of that. They can't fix themselves without outside aid because to them there's nothing to fix.