Radishes. Everyone says "They're easy! Grow them with your kids!" and sometimes they don't sprout, and sometimes they sprout but don't radish, or occasionally they do radish but only very small bitter rocks with worm holes in them. This year we gave up on watermelon radishes and are going for something with a short time to maturity, and they've sprouted and are making true leaves, at least. So we'll see.

(Hi, I'm Miriam, and I'm new here.)