And maybe tell their mom and dad not to bring them back if they can’t respect you or your animals? That is something you definitely wish you could say.You're not punishing them, you're protecting them. Same as you would if any predator was in the area. That's your job. These kids may not actively harm your chickens but they are definitely stressing them. Perhaps teach the children that they can watch the chickens if they sit quietly in little chairs that you provide, and point out interesting things about the chickens. Maybe teach them their names and see if they can learn to identify them, unless the chickens all look the same. Best wishes!
