When my wife was pregnant with our first child, I had a family member tell me that when his first child was born, he became much more sensitive to all the evil in the world. I experienced the same conversion when Carol was born. The operative principle appears to the be the intense connection that I feel, as Carol's father, to her state of wellbeing.
When I see Carol running about our home and she has a really close call with injuring herself, the anxiety I feel is palpable---it's a physical sensation. When I see Carol actually injure herself, that's something physical too. It's not just a thought or an emotion, it's in my flesh. Her vulnerability is my vulnerability.
I have the same physical sensations when I think about all the opportunities for Carol (and now Anna) to be injured outside our home (referring back the "evil in the world"). Our culture is not very kid friendly and on some levels is actually kid hostile. There are forces shaping our culture that are not so concerned about vulnerable persons as they are concerned about self-gratification.
I think solidarity with vulnerable persons (children) is one of the graces of the Vocation of Holy Matrimony. It's a powerful grace because it isn't confined to one's own children---it reaches out in all directions and deepens your connection with the human family.