Those are cabbage aphids and they adore kale!! It is easiest to just hose them off with a strong stream of water. Otherwise you can treat with insecticidal soap or Neem oil, both of which are acceptable insect controls for edible plants. Another means of control - although it may be problematic at this time of year due to lack of availability - is to gather up some leaves from a tomato plant, chop them up finely and let them sit overnight in a pale of water. Then spray the plants down thoroughly. This releases toxic alkaloids in the tomato foliage that aphids find distasteful and they will stay away.

When spraying anything other than water on edible plants, natural control or not, be sure to wash the plant thoroughly before eating.

I treated the plants with this tomato-leaves concoction and the aphids appeared to have a tough time resisting it. I hope this does the trick. Thanks for the advice!

I feel your pain. The Aphids have become a real problem here in my area and they have become resistant to more and more insecticides. The big problem when using organic sprays is coverage . If you miss the underside of any leaf that has eggs or aphids the breeding ground is still there. You would need a pet mouse and a miniature tractor with a spray rig like they use in the orchards in order to get 100% coverage and kill the pests. I have moved to using " Bayer Advanced Fruit, Citrus & Vegetable Insect control" It works great and now I have zero problems with aphids. You inject it in the soil around the base of the plant with a garden sprayer. It only takes one application and it's way cheaper and less time vs spraying neem oil over and over again.