When I brought adult, ten year old, Zenobi (otb) home she loved my second storey balcony. Then a few days later she disappeared, I looked over the edge and there she was on the ground. I hurried downstairs to see if she was OK.
She wandered in a bit dazed and looked up at me as if to say what kept you. I put up some wire fencing lashed to the railings. What I think happened is that she saw something, an insect, a bird, another cat, and over-reached trying to get at it.
Maybe she was just lucky with her fall, but I suggest taking precautions. Most cats do land on their feet, and cats spread out a bit like a blanket, which no doubt slows a descent, however, everything in life does not always happen the same way, and your if kitten happens to fall the wrong way....