Womb twin kids - when the rest of the family looks on in silence

When it is clear to you that there is a young womb twin survivor in the family, and no one seems to be talking about it, what can one do?  This is a problem I have had from the beginning, ever since I learned how to recognise a womb twin survivor.   I notice womb twin survivors  all the time now - people of all ages, but when the individual concerned is a child, I badly want to speak out.  But should I?  Should anyone?  Should we speak out or remain silent?

It seems that there are several reasons why  its NOT a good idea to mention it...

1. Parents may be sensitive to implied criticism, as if there must be something wrong with their child.
2. The usual scepticism about the possibility that  the loss of a twin early in pregnancy can possibly have any kind of effect on the child who survives.
3. Its a private matter and no one should interfere with how any parent brings up a child.

(Of course I  have an additional problem, in that as founder of Womb Twin  I would think that, wouldn't I? People groan every time I mention it... Not again, they cry..... understandable enough I suppose.)

But there are more reasons why its worth mentioning, but how?

1. Its best for the child to know.  My research seems to indicate that the children who know do better in life than the children who are left wondering why they feel so strange and different. 
2. They already know, at some level.  This film is a good example :

3. This is a very important piece of personal information and the child has a right to know.

What do you think? What is the best way to tell a child about their twin?