I fully understand the desire. Even if they added this, it would have to be an option which you could use your agency to enable or disable - so why add the option when your agency and the existing phone features would work just as well?
I'm thinking a polite reminder from the teacher + the example and teachings of their parents + counsel from an apostle* + agency might be a better option.
*
https://www.lds.org/broadcasts/article/ ... d?lang=eng
"And consider putting your smartphone or your tablet in airplane mode for the entire Sunday block. You will still have your scriptures, general conference talks, hymnbook, and manuals, but you will not be distracted by incoming text messages or push notifications."
"Be Still, and Know That I Am God" by Elder M. Russell Ballard
If it's really needed, you could take a part of a class to teach all the students how to do this, checking that each one understands how to follow the counsel of an Apostle...
Just my opinion.
Liz