I don't know if anyone else has tried kohlrabi yet with their babies, but my son loved it! I'd never really tried it until I moved overseas. I know it is somewhat available in the US and the UK.
Kohlrabi tastes and has the texture similar to a broccoli stem but it is a member of the cabbage family. They sort of look like a crazy space satellite (especially if you buy one without the leaves). Wikipedia has a great article on it here.
If you've never prepared a kohlrabi, the easiest way to do it is to start by slicing of the woody bottom, and then using a vegetable peeler, peel off the rest of the skin. Then you can dice it and steam it (or do a stir-fry! mm!).
For my son, I steamed both the vegetable and the leaf and pureed them together. He really liked it and I'll definitely make it again for him.