Eye open in 3-4 day old kitten!

The rescue I foster for got a call yesterday from a woman who had found three very young kittens in her yard and the mom had not been seen in a day. I'm not sure how old they are but the lady first saw them on Tuesday, with the mom then. I suspect that they were born on Monday or Tuesday. It's Friday today.
I took the kittens home and put them in with a litter of ten day old kittens and their mom. The mom is now caring for them and they are doing fine. However, I just picked up one of the little kittens and saw that one of his eyes is open. They should not be open for another week. Can this be harmful for his eye? I've never seen this before.
Not that I think that it has anything to do with it but the older kittens, the now eleven day old ones, have just opened their eyes today.
Is there anything I should do? Any tips or insight would be great.

Thanks

If the Mom was a severely undernourished stray or sick during pregnancy the kittens could be older than you would expect from their size.

I don't know how much the mother cat has to do with the eyes opening, if her washing, etc. has anything to do with it then she may be treating them like she does her older litter and thus causing the eyes to open?

My kittens had their eyes open starting at 4 days it isn't uncommon at all.

Leslie

We have several kittens that opened their eyes within the first few days and they're grown up and healthy. I wouldn't worry about it.

I've had kittens born with their eyes open. Like the above posters have said, it's not uncommon.

My rex kittens has eyes opening by 5 days old. Its not common to be less then 5 days, but it happens. The average is 5-14 days for opening eyes.