Interestingly dumb phones are making a comeback.

They disappeared for a few years, but now you can buy a dumb phone, for example running KaiOS, that charges with USB-C and supports modern cell networks. You can even get a Nokia!

There is absolutely no need to buy a smartphone to any kid younger than 15. Now for high school students it's a bit different, they should be old enough to have self control and respect rules to keep their phones in their bags during class.