It's written in every lab, I think. I looked into it myself because we have 1-1.3m L-bricks on the terrace. Basically, I didn't want to have a guardrail, and even though my children are already older, it becomes much more problematic with visiting children because, insurance-wise, if something happens, no insurance would pay out. Whether it's a broken leg, follow-up treatment, or "falling on the head" and becoming a care case for the rest of life.
Your hedge, even if it gets bigger and denser, is not considered fall protection insurance-wise, because it's not only about the height but also whether a child can stick their head through and fall through. I think the metalworker said something about 15cm between the bars.