Last year, my first with chicks, I gave provided free choice grit at about a week old. I plan to do the same this year.
I used chick grit last year until they were 12 weeks old. Then I switched to #2 size grit. They sell it in four sizes. #1 is for chicks. #2 is for all of chickens over 12 weeks old. #3 is for large/standard breeds when they reach full size. #4 is for turkeys. I selected #2 so that I could buy 1 50 lb bag. It was only $9.00. The people at the feed store said this size was fine for their entire life (after 12 weeks). So far I have used maybe 1/4 of the bag for my 15 pullets. They are almost 1 year old. I suspect this bag will last me at least another year even though I am adding 25 more chicks this year.
I give my week-old Goldens a small pinch of polenta (medium corn meal) along with a pinch of fine sand from the run they will eventually be in. They don't get much, but they enjoy pecking and scratching for it in the brooder. It gives them something to do, and fine sand works great for them. Their little gizzards aren't very big at this point but it is there, and anything that goes through it besides chick starter requires grit.
My opinion only, and based upon what I have read, starting your chicks on a bit of grit right off the bat will virtually guarantee they never develop "sour crop" and several other digestive problems. As long as they have good "though-put", feed 'em!