I've been giving my chicks small amounts of treats every day since they were about 4 days old. I also offer free choice chick grit. They seem to be thriving and ever growing. They are now 2 weeks old and nicely feathering in. I have had no issues of pasty butt, impacted crop or any other digestive problem. Their poops are normal and frequent. I have to add that I also give them Apple Cider Vinegar in their water.
It's a matter of personal opinion, I think, and you'll get varying responses. You just have to do whatever you feel comfortable with. The reason I give them treats (in the form of greens, mealworms, yogurt etc) is that they would be eating that with momma hen if they had been brooded with a hen, so I figured it wouldn't hurt them if it was done in small amounts. I also find that it keeps them as well as me very entertained. But a little bit goes a looong way with chicks this tiny.
