If they have never been outside then it can't be mites...sorry I reread your first post and must have missed it. Later if you get mites, you can use Poultry Dust from the feed store and dust them and the coop. Retreat in 7 days for mites and 14 days for lice. But I wouldn't do it on itty bitties "just in case" or in chickens who are still in the brooder.
Since they are silkies, I'd do the vitamin thing for "neurological silkie" symptoms.
I'd buy a poultry vitamin pack...either avian pack from jefferslivestock or from your feed store. This may help them...I don't know. Many times silkies do odd "neurological" things and vitamins help.
Here is a nice link if you ever have to deal with wry neck/crookneck in your silkies later on. Also some nice silkie articles:
http://browneggblueegg.com/Article.html
on left column you can click under "silkie skull" and "crookneck" to read some articles about silkies
Shows a pic of the silkie skull if they have the huge vault (open spot in head like a baby).
If you are against artificial vitamins, you can simply feed them scrambled or chopped boiled eggs....very nutritious and perfect chick food! Also good to give them very short grass clippings, about 1 inch long for vitamins.