Ok, so quite literally it seems like a parent has lost their child, he was taken from them 50 years ago and they still haven't found him.
But I can also think of two deeper meanings:
It could be that the person was molested as a child (or made to kill someone) and as a result, their childhood was taken away. Now they've become hard and cruel, possibly a killer. They are searching for that lost child in themselves through different experiences around the world. But have never managed to find something which makes them believe their inner child is still alive.
Another could be that the person (who is in his old age) is looking in the mirror and talking to his innocence, his childhood. He did something because of which all the innocence in him died, now he is looking for it but cannot get it back. He has done it to himself and hates himself for it. He wants to be this warm and compassionate person and start feeling again, but cannot. But he still has hope that before he dies, he will get a glimpse of that child in him that he never ever found.