My kale is now covered. I bought some galvanized stainless wire and made hoops and then covered them with row cover and secured with plastic pegs. I picked a good batch of it a couple weeks ago (photo below), but ended up composting it because there were too many holes in the leaves for it to be appetizing. Hopefully the cover will help. Of course, it doesn't get rid of the caterpillars that are already on the leaves. It just prevents the moths from laying more eggs.
On the far side of the covered kale are my baby broccoli plants. These are also being eaten, presumably by the cabbage white caterpillars. I will have to cover these plants too. My next project....
I looked hard, but didn't find any green caterpillars. Since I have noticed many cabbage white butterflies, I assume this caterpillar is who is eating my brassica. The caterpillar I did find is pictured below. It is tiny and like an inchworm, but I don't know what type of worm it is.
Kale (Brassica oleracea, Acephala Group)
cabbage white butterflies (Pieris rapae)