However, I came across the writings (letters) of the very famous and respected Russian elder, Father Ioann (John) Krestiankin, who repeatedly said that we should not pray for the unborn children, and that it is even blasphemous to do so!
Unfortunately, I can't find quotes in English for what he wrote, but I can say that I found the quotes in the book which is a collection of his letters. The Serbian edition of the book has letters from three different books in Russian. While I don't speak Russian, if someone wants, I can try to type the title of the original books here.
The most important quotes about this issue from Father Ioann (my translation from Serbian to English):
What does that have to do with blasphemy? And why is "human form" important, I thought that Orthodox Church regards even embryo as a human being, so why is physical form of importance? Notice: this letter was sent to a woman, so the words "you can't pray for unborn children" can not be interpreted as "you can't mention them at the Liturgy, but you can pray in private".
I want to warn you immediately, that is, to tell you that you can't pray for unborn children, who did not come to this world in human form. That would be blasphemous.
Or this quote:
This second quote is taken from the third letter on this page (translated by Google). Basically, in that letter, the elder mentions a particular prayer which was supposed to be read for children who died at birth, or due to some unexpected circumstances. "It is intended, therefore, to those who have died by the will of God's providence and not by the will of the mother - offenders." Why is this important? A dead child is a dead child, why should the answer to the question "can I pray or not" be based on the cause of death? Can anyone offer some insight on this?
If a child was not born due to the evil will of the mother, then it should not be prayed for those lost children who didn't even get human appearance (they didn't even get to this world).