I would use it. When I use corn, I prefer to apply it in smallish amounts and after the birds have crops already close to full. If to be offered free-choice to totally free-range chickens, it can take a few days before they start to target other food items to balance out the diet.
Mine love it. A favorite treat I use to get them in the coop if I need them out of the run or need them to come in from free-ranging. If they see me with the "treat mug" that I use, the literally all come running (hopping...catching some air!) for their corn! And yes at that age it is fine for them to have as a treat. Do they have access to grit as well?