I'm sure it doesn't apply anymore but 4 future reference sleep in kittens eyes r completely normal. When they get sleep in their eyes then grab a wash cloth or paper towel, turn your hot water on, soak some of your wash cloth/paper towel, let it cool down (don't want to burn their eyes, but make sure it is warm so it slightly melts it), gently massage the gunk in circular motions. Make sure everything you use is clean & don't use anything even remotely sharp bc they do have a tendency to jerk their heads. There really isn't anything you can do, it'll pass, but you can always bring them to the vet & they'll give you antibiotics & possibly eye drops. Do not use human eye drops, never give animals human stuff. Their bodies r made differently & even the smallest sliver, or drop can cause death--always consult a vet, best to get 2nd opinions too.
It is very common for kittens to get infections in their eyes soon after they open. (it may get scratched by a hungry sibling) The eye seals itself shut from the discharge and can be gently cleaned with warm water on a cotton ball. If the infection does not improve you can get some erythromicin opthalmic ointment from your vet. This will take care of the problem quickly.