I'm really new to this, so maybe I just got lucky, but I just bathed my smallest Silkie yesterday, at only 5 days old. It was covered in all manner of grossness from the other chicks and I was worried that it wouldn't stay warm enough since it's feathers were all matted.
I simply ran it under the faucet (keeping it's head dry) in water slightly warmer than lukewarm, didn't even use soap. I gently rubbed it's wings and body under the water in the direction the feathers grow. I then patted it dry with paper towels and held it under the heat lamp for a few minutes while blowing on it to help fluff up the feathers. In no time, it was dry and fluffy and scampering about the brooder. It seems much more comfortable now.
If you do decide to wash them, I'd make sure to just do one at a time so you can give each one lots of attention and make sure they are reacting well before moving on. Good luck!