Wait until they are fairly old. I love feeding my chickens table scraps, the only problem is that they can sometimes dilute the amount of protein in the diet, giving them a protein deficiency. So make sure the food you are giving has 20% protein, and you feed plenty of egg scraps, and meat scraps with the leftovers, as long as the meat doesn't have to much salt. Pumpkin seed are also good to feed them every ounce and awhile. Good luck with your chickens,
Avery
I bought about a 2 gallon bag of granite grit from the local mill, they put it in their chicken scratch. Ran it thru a colander with 1/16" holes. Bagged the smaller stuff for the chicks and sprinkle some over a chunk of sod in the brooder during the second week.