Had to look up sea kale. Don't think I have ever seen it.

I agree with Patsy, casseroles, hot pots, etc. are one way to sneak some vegetables into children's diet.
However, we often had stuffed peppers, and they were accepted.

No problem with tomatoes as long as they were in the form of sauce in pizza! Tomato soups were accepted, as well as the small raw tomatoes we grew.

Parsnips work well in stews, etc., but I won't eat them solo.