What is "Re D"?
I hope someone is familiar with British legal matters.
What does "Re D" stand for in this article?
https://www.mjc-law.co.uk/female-majority-in-the-supreme-court-re-d/
Female majority in the Supreme Court – Re D
In what will be an important and ground-breaking decision, the case of Re D was the subject of an appeal before the Supreme Court last week.
The case concerned D who is a 19-year-old male...
I suggest you look up Oxford Dictionaries or something like that. The pieces you cite are clearly legal papers: so you might also try googling "legal meaning of Re" or something like that.
In fact, Dictionary.com has a fair definition of the word.
...Re2 preposition Chiefly Law and Commerce. in the case of; with reference to; in re.
ORIGIN OF Re2 1700–10; < Latin rē (in the) matter, affair, thing (ablative of rēs)
I do not think the explanation is quite right, though. It has the correct origin, from the Latin word Res, meaning a thing or, in the law, a matter (meaning the particular case being dealt with). It is not a strictly preposition, however, although it is, in a sense being used prepositionally. The whole legal Latin phrase is in re, meaning in the matter of. Re is, as the definition says, the ablative case of res. From there, the phrase in re is often use in shortened form re meaning about or concerning. The word Re is frequently used in the heading of formal correspondence to indicate the topic to be covered in in the letter. So you can have:-
Re Your Letter of May 16th; or Re Purchase of Flat Iron Building NYC
Going back to the first document, the letter 'D' refers to one of the persons involved in the legal case being discussed, who is not being mentioned by name, presumably to protect anonymity.
So, "Re - D" is brief a way of saying: "Concerning D" (whoever D is - presumably known to the relevant lawyers.)
First, for the purposes of following this article, it is sufficient to understand that Re D is the name of a court case, and thus of the judicial opinion rendered in it; it is not necessary to know why the case has that name. It is quite normal to refer to legal cases by their names, without giving any thought to why they are so called. This is because what makes a legal case important enough to be referred to by those who are not directly involved, is the general rule of law that is articulated in it, not the details of who was involved. Millions of people watch movies and television programmes referring to Miranda-rights without ever pausing to ask who Miranda was and what he did; their appreciation of the story is not at all affected by their not knowing anything about him. Similarly, there are many political debates in the United States about Roe v. Wade, but very few of those who participate in them would be able to explain who Wade was and why he was the respondent in that case. This is quite natural, because the importance of the case as a precedent is not affected by such matters.
Second, if one is nevertheless curious why this case is called Re D, the answer, as has already been explained on this page, is that it is a case concerning somebody who is referred to in the court documents as ‘D’, because the court has decided that the person’s full name ought not to be made public. What the other answers on this page, however, do not explain is that a case name beginning with Re, or in some jurisdictions with In re, indicates that the case (unlike the majority of legal cases) does not involve a dispute in which one party is suing another. That’s why the case does not have a name of the more usual, Smith v. Jones kind.
'In re' means 'in the matter [of]'. See https://en.wikipedia.org/wiki/In_re. And 're' thus means 'the matter [of]'.
I would guess that D is the first letter of the child's or juvenile's last name (or of somebody whose identity needs protection for other reasons).