I think the kiwis would be alright but you may want to look around just to make sure they are safe. Chickens are like little fluff balls that fill up that little space in your heart and never leave :)
p.s. You might want to try chopped up strawberries too. My chickens love those and they work...
First of all, you should start adding grit to food when they are about 3-4 months old. Feeding them a little bit of grit as youngsters wont hurt them but try not to use it more than twice a week. Also, grit should be added to things with grains, corn, seeds, ect. The grit does not need to be...