Do you let your kids drink caffine?

I am talking like soda or iced tea. If so what age do you let them start having that kind of stuff? I let my 7 year old son have sprite as a treat when we are out at a restuarant but that does not have caffine in it. I just cant seem to let him have the caffine yet. Now my almost 3 year old sneaks my diet coke every chance she gets. It makes me so mad. I just dont know when its ok for the kids to start having soda with caffine in it.