It's the child's behavior that needs to be changed here....
....pretty hard for one so young to understand how to behave around livestock.
I have to support this comment.
Its right that you shouldn't punish the livestock for what the kid did. If you do, the kid won't learn. And it brings more trouble in other ways.
An example is my town has tons of people who have had relatives kicked by horses. (Really this is awful.) But the whole thing is mitigated by telling kids, 'don't walk behind the horse. Don't spook them', etc. This is why they should learn very early to be careful around animals; because animals can cause injuries. I've heard people have to be careful around rams for example, even though sheep and lambs are really sweet animals.
To be fair, also I've had my brother chase my ducks around. He is over 20 years old and knows better. And it kind of ticked me off. At the time they were 4 week old ducklings, and its the brother that doesn't like me. So I think he maybe had some mayhem factor in it. But I'll never know really.
It worried me a lot though, because they were small.
People with respect for themselves and others you will see will almost always take a minute and coach their kids how to act around animals. So I do think this can be fixed. And I think the poster is someone with self respect and family values also or they wouldn't have asked this.
SO here's what you can do...
You could have the 6 year old future chicken abuser try feeding treats to both the rooster and the hens. This should help him get their trust back. But the first few times doing it, I'd take it slow and chaperone him. (Have him do it out of whatever container the chickens AND rooster normally see you giving their food in. This will help.) Do treats they like. Peas work well with ducks. Some are going to say mealworms. Oatmeal makes poultry crazy, especially cooked. You could try those, and you don't have to buy anything special.
And kids like doing stuff like this. So its a win win situation. Kids like to be helpful at that age also, and its a great time when they haven't learned to resent authority or chores yet. And they want to prove themselves to an adult that is showing them a bit of attention.
So this can be a great opportunity. It could also be an opportunity to get them interested in future agriculture projects and teach them where the food and the feed comes from. And how their food gets on the breakfast table.
I believe it can be turned into a really great opportunity for you.