So the correct answer is to tell your kids to tell them to get fucked and call you. At that point, remind them that the device is your property, decline their request and they can only threaten you, which is 100% illegal.
I am more worried about the teachers from experience than the other students. Some of them I have encountered over the last 15 years of having three kids at school have been right nasty pieces of work and should not be in a position to have power over a minor.
Teachers have many of the same powers over children that their parents do. Power to detain, to punish, and yes to search.
If you're not happy with that as a parent then you can home educate them instead.
Also, your argument is pretty much "if you don't like it just leave". Which is one of the worst arguments for pretty much anything.
im telling you, the police will not like that policy any more than the students.
you're in a school. you don't have the right to do whatever you please.
With that said, I've got no idea what schools should do about things like sexting.
If I was a teacher and I confiscated a phone which might have illegal photos of underage students on it, I wouldn't want to turn a blind eye to that. But I also sure as hell wouldn't want to search it myself. I'd want that done by someone of unimpeachable character.