Kitten eye infection ? ?

Okay so my cat had kittens 4 weeks ago (the mom was a stray and we found her pregnant and we already made an appointment to get her fixed once the kittens are weaned) but anyway she has 3 kittens they are all doing well and are walking and running around just fine. Their eyes opened when they were about 2-2 1/2 weeks old. But one kittens eye ha always had a little trouble, sometimes it would be crusted shut and I'd open it with a warm washcloth. At first I thought it was just goop from their eyes just opening but then the other ones didn't have this problem. And now there's like yellow goop coming out of his right eye daily! I wipe it out a often as possible but it's still coming! We've made appointments for their regular 8 week check-ups and my mom can't move it up any closer. Soo I was wondering if there is anything I can do in the meantime to stop it or prevent the other 2 kittens from getting it? Thanks in advance :)