It would make sense. No matter what the law becomes, these measures need to be taken to support protected people and to help them understand their obligations.
However, I would say that while “substantial harm” is defined in the legislation, the criterion is not substantial harm. The criterion is potential substantial harm. It could result in substantial harm. You're asking a 15-year old to think in advance, “What I'm doing now, sending a tweet, might result in substantial harm”.
The text is “could result in substantial harm”.