J.R.R. Tolkien, in (I think) On Fairy Stories made the point that children are not a special class of people (akin to women, men, Englishmen, Americans, etc.), but just people at a particular stage of development. Which is to say, it’s misleading to say “children like this” or “children do that” just as it’s misleading to say that about people in general. Children have all the same variations as adults, because they are the same people, just encountered at different times.
Likewise, of course, trying to claim than unborn person is not a person has no leg to stand on, because that’s simply what a person looks like at that particular stage of his development. The first period of someone’s life is spent unconscious and inside his mother; that’s just how people are (rather like how the earliest stages of human existence was spent with no form of writing or record keeping save for oral traditions, leaving it a mystery that can never be fully solved).
And likewise, the Church on Earth is just what the Kingdom of God looks like in this particular region of Creation. The Church Militant is not a separate entity from the Church Triumphant; it’s just the local branch. In fact, in a sense this world is a part of Heaven, just the earliest and most basic form; the womb of Saints you might say. As soon as we are Baptized and enter the Church, we have in a sense entered the Kingdom. Just we’re in one particular part of it.
Basically, just as we shouldn’t think of children as separate entities from adults, so we shouldn’t think of the things of this world as being completely separate from the things of Heaven. Rather, we should try to view the things of this world in the context of its being a part of the Kingdom of God and the threshold of eternal life.