Please help… sick kittens?

2 weeks ago a stray momma cat moved into my chicken barn. I cant touch her and the only time I can get close to her is when she’s eating the cat food I’m giving her. Then I noticed she has 3 kittens with her. Old enough to eat cat food but I still see them nurse. Today was the first time I could get close them and all 3 of them have extreme discharge coming out of their eyes. To the point of their eyes almost being sealed shut. What is this caused by? What can I do to help them get better?