Potential fragility aside, I think flip smartphones (at least the cheaper ones without a proper outside screen) solved the problem for me since I was never really a one-handed user of my XZ1 Compact. I liked the smaller size because it fit into every pocket safely and the smaller screen was more annoying to use and therefore less addictive. Flips have a similar barrier in terms of having to physically open the device to use it. It’s a shame that even the cheaper models are getting the bigger outside screens now, though. It just makes these devices more addictive and more fragile.
Depending on where they live, it could be more likely their first phone is an iPhone.