It sounds like it could be a louse you saw.
I would suggest you buy some 10% permethrin and dilute it per the label to treat first the coop then the birds.
You will need to completely clean out their coop. I would also vacuum the crevices with a shop vac then spray all surfaces of the coop with the diluted permethrin (including the tub of the shopvac). Pay particular attention to all areas that form a crevice and don't forget the nest boxes. Mixing up the solution in a garden pressure sprayer is easiest. Allow the coop to dry naturally then add fresh bedding.
Then use the diluted spray to spray the birds down to the skin in the following locations: under the vent in the fluff, under each wing, at the base of the neck and tail and on the chest.
The easiest time to treat the birds is to grab them off the roost at night and wear a headlamp so both of your hands are free to handle the bird and the spray bottle of solution.
The entire coop/bird treatment will have to be repeated again in 7 to 10 days to kill adults that hatch from any eggs that are on the birds/in the coop.