My goal is for them to learn. And yes, I can just carry on, and some will cheat. I've caught cheaters in the past, of course, but they were far and few between. With ChatGPT and even improved translators like DeepL, it's hard to get them to do the practice they need to learn.

And as a teacher who really WANTS them to learn and to get that feeling, "Hey, I can actually do this!", it's depressing to think of the one who do cheat themselves. Oh well...

Just tell them, "the point of this exercise is for you to practice writing in English, not for me to grade you. If you use ChatGPT to do it for you I won't be able to notice, but it will be pointless. It's better if you don't do it at all than if you do that."

Teens are very propense to succumb under peer pressure. Some would be honest and do the work themselves, but if a significant subgroup is using GPT there's a bigger chance that this group influences some of them to do so.