S.C.
I say leave it alone. Most of the time the Mommy kitty will lick that junk off the kittens eyes. We had a barn kitten that had that crusty eye stuff. I kept trying to clean it and it wasn't doing any good. I left it alone for a few days and it cleared up. Try not to handle them too much until their eyes are open. I don't know if that's a factual thing, but my Grandma always told us to leave them alone till their eyes were open.
You should probably schedule vet appointments for all of them anyway. Maybe have the vet take a look at it if it's not cleared up in a day or two.