My kittnes are a little over a month old and one of their little eyes are a little red and they have a greenish mucus discharge. Will visine clear it up?

Take them to a vet.

Visine is a mild eye anti-irritant but has no antibiotic properties at all and will be quite irritating in an inflamed, infected eye. The greenish discharge is pus, and it is strongly indicative of an infection from either a virus or a bacteria. Several bacteria produce a characteristic pus color, but it may not be necessary to identify the particular germ, since most eye antibiotics have a wide bacterial spectrum activity, but unfortunately absolutely no effect on a virus. That takes an antiviral medicine.

The point of this is that you need a vet to prescribe the proper eye medicine. Untreated, persistent eye infections can cause a variety of damage to the eye from pain and swelling to ulceration of the cornea and even blindness if the ulcer ruptures.

Until you can get to the vets, you could also clean the eye with a warm, moist tissue. Normal contact lens rinse solution (saline solution) can be used to further rinse the eye, BUT, do not use the solution from the container you use for the cat in your own eyes afterwards because of the possibility of it having been contaminated. If you do clean the eye and notice that the cornea is milky colored in a spot, or all over, this means the cornea is being attacked and has, or will soon have an ulcer on it, and is an even stronger indication of the need to have the vet see all the infected kittens.