If you notice any swelling/bulging under the eyelids, you should open them gently with a cotton ball dampened with warm water (DO NOT use Q-tips). If you see pus dripping from the eyes, it is probably an infection and the kittens should see a vet. If the eyes remain shut after 14 days, your vet should look at them. Other things to look for:
Kitten's Eyes Were Open BUT Are Now Closed
I have 4, 16-day old kittens, and their mother, but one of my kittens never opened it is left eye. And just this evening, I noticed that another kitten, whose eyes were open before, had one of its eyes closed. I was thinking it might be an infection, should I apply boric acid? ~Concerned
I would recommend against your applying any boric acid to the kittens, as you could risk blindness. If you would like to clean their eyes, consider using a cotton ball, moistened with saline. With it, cleanse the outside of the eyelid very gently. Do not penetrate the eye or go behind the eye lid.
What you describe could be an infection, although only a vet can make the call. A visit may be worthwhile. Simba