Question about eyes opening

Well today Bella's kittens are 9 days old. All three kittens are doing great and looks like they have doubled in size. I have a question about their eyes opening. It looks like their eyes are beginning to open. One of them you can see little slits now and the other two it's like they are starting to move their eye muscles. The one kitty that looks like his eyes are open a little bit it seems a little moist. Should they open gradually or all at once? Is there anything that I should watch for or anything that I should do to prevent eye infections. I have never had kittens before and I just want to remain extra cautious. Thanks in advance.

Watch out for eyes being stuck shut, swollen eyes, and puss. This is a sign of an eye infection. All 4 kittens in my litter had eye infections and they cleared right up with terramycin eye ointment which my vet recommended and you can get at any feed or farm store. To prevent them just keep the bedding very clean. I'm not sure why mine got eye infections I kept their bedding very clean and sanitary.