What to do if chicks/ducklings have been fed veggies for several weeks without access to grit?

[Mirrium]

Let these people know that it is NOT ok to feed chickens celery unless it is finely diced. the strings can get caught in their craw. Myself, I would not allow them to feed MY pet chickens at all.

I've tried telling them nicely, I've tried yelling, even messages. Nothing seems to get through to them