Actually, given the opportunity, baby chicks and they will start "dusting" right away.Though I think it's pretty much worthless against mites or worms DE is perfectly safe for dusting or eating.
Off.... your.... rocker.
We had a horrible infestation of mites in our coop for a few weeks. I dusted the entire coop down, put some DE in the food and rubbed the chickens vents with DE (where all the mites were congregating) and did nothing else. 2-3 days later there were no mites and we still don't have mites to this day.(3 months later)
DE is worth it not in my opinion... but in my experience.
Edit: Sorry to hijack the thread. To better answer the question I wouldn't see any reason to give chicks DE except for dust bathing. I wouldn't think you'd have mite issues until they're much older.
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