Yes chicks and chickens don't need grit if all they eat is chick crumbs or pellets. As soon as they are exposed to any other foods they should have grit. However if they free range, they don't really need it. If not, provide it in a separate dish or container near their food container.
If you offer anything other than crumble to chicks they need grit. Ie worms, seeds, etc. You can purchase chick grit or pound up what you have for older birds. Older birds will forage for small rocks etc but I provide grit for my flock. I just dump it in small piles here and there in my yard and let them use as needed. You can also use a dish.
I have always started within the first few days. I was told to sprinkle like salt on their feed until they are older. They may be only eating chick feed, but they might also nibble on bedding, depending on what you use. Better safe than sorry & has always worked for me.
When my chicks were about a week old I wanted to start giving them meal worms as a treat, in order to start taming them and teaching them to come to the sound of my voice. So about two days before I introduced the dried worms, I put some chick grit in the brooder, in a heavy dish they could not tip over. And I was amazed, they gobbled up that grit the way I go after chocolate chips! I guess they know what they need!
I mix Chick Grit in Start and Grow feed starting at 2 weeks old at a ratio of 1/40.
2 ounces of grit by weight to 5 lbs feed. 10 ounces grit to 25 lb feed. I weigh grit with a kitchen scale.
At 7 weeks I offer Poultry Grit in a separate container.
.Chicks do eat pine shavings. GC