Yes, the calcium is there all the time. Keep it from getting wet, and it'll be fine. It wouldn't grow mold unless it got wet and dirty.
Keep anything that isn't their feed (or the calcium) to a minimum, as yes, it would be a treat.
I make my chickens "work" for their treats. When I give them a...
These are NOT dumb questions. We were all newbies at one point. It shows that you're thinking ahead and planning. :thumbsup
Here's the reason behind the all flock feed ("flock raiser" or "flock maker" are other terms for essentially the same thing).
Look at the protein levels in a layer...
I think they'll love it.
For my last batch of chicks, I'd sit by the brooder with my feet in there. They were scared at first, but then realized that "momma jungle gym" was fun.
When reaching for them, always reach from the side, never from above. They are instinctively afraid of predators...
An excellent "treat" at any age is their regular feed, wetted into a mash. All of my birds have loved it, from the first time they got it at about a week old. Chick feed doesn't require grit, but you can leave a small dish of chick-sized grit in the brooder for them.
Mash snack is also how I...