Puff them again in about a week. Also you need to clean and dust the hen house because the lice can be in the bedding.
I would dust the broody. The chicks will get powdered by being under her wings. I think they will be fine. i have never had to dust babies before.
I use a mix of sevin dust. I take an old panty hose and cut off the foot. Put a good bit of the dust down in the toe and tie it off. Then I use it like a powder puff.
If you will hold them upside down and then puff it all over them you will be sure to get it down in the feathers next to the...