Have Cat Questions? Ask a Cat Vet Online.
You can wash the eye with warm saline to remove any debris that might be causing it.
Then you need to see your vet tomorrow. The good thing about a litter of kittens is that the vet will often see them all and only charge you for one office visit. If this is a concern for you, be sure and ask before you go.
Let me know if you still have questions.