I wonder if you had/have pill bugs and/or slugs. Aphids don't eat plants, they leech juices from them. Pill bugs and slugs (and other critters like caterpillars) actually eat foliage. They ate all of my lettuce sprouts last year too.

The best way to prepare soil for gardening is to add some compost to the surface.

I should have been more clear and not said "ate". They shriveled them up and turned them to mush. I could see the aphids, so I knew it was them. We do have slugs too, but I try to keep those at bay and they were not a problem with the kale or cabbage.

I brought in a load of compost in October and they were planted directly in to that mixed with some sand/topsoil that we already had. My entire garden is black with compost, so I think (I hope?) I'm good there.
I have been thinking of going out and planting some test peas (aphids got those late last winter) in another bed and seeing what happens.

Thanks for your reply!

Good soapy water will kill your aphids as well as the ants that bring them. They ants are your problem, get rid if them and your aphid problem will go away.