I think the part of being a Boy Scout where you are an older teen and expected to look after the younger children in the troop had some of this effect on me. I am bummed that Boy Scouts has collapsed for poor leadership reasons.
I definitely experienced some version of this at the birth of my child. I was convinced, even while I knew it was likely not true in the outside view, that my baby was actually the cutest baby. My child is not genetically related to me, so I don't think this was a matter of calibrating my standards for cuteness on other babies in my family or on similarity to myself. Also, I definitely have a persistent increased tendency to cry during movies, especially in scenes that involve the separation of parents and children.
I do have a sibling 4 years younger, and have always generally liked babies and children, but this was an additional effect.
I agree I've felt something similar when having kids. I'd also read the relevant Paul Graham bit, and it wasn't really quite as sudden or dramatic for me. But it has had a noticeable effect long term. I'd previously been okay with kids, though I didn't especially seek out their company or anything. Now it's more fun playing with them, even apart from my own children. No idea how it compares to others, including my parents.
I did not experience any changes like this at all when my daughter was born. When a child myself, I loved younger children, but as an adult I've not been very keen on young children, and I'm not particularly attached to my daughter either.
This is actually one of the many reasons I don't ever want to have children in the future. I am very wary of the idea of being forced to care more about a specific person or group of people than about everyone else, as it seems very unfair to me - and also I think that our society massively over-fixates on a rather ill-defined goal of protecting children, which often ends up smothering them (helicopter parenting etc), and I don't want to be tempted to do that.
I certainly care about them in abstract as you describe having done before - but if I got too emotional about it, I feel like I'd make bad decisions that were more rooted in "feeling like a good parent or parent-like-person" than in what is actually best for everyone.
Are you saying that you think that you in particular would be unusually prone to over-fixating on a child of your own, smothering them, and making other bad decisions? If instead you think that this just a common failure mode, not one that you are especially prone to, why would you think that future children would be worse off with you as a parent than someone else?
As for thinking it unfair for you to care more about a specific person than about everyone else, have you thought through how your notion of fairness would play out for actual children? Do you think there is no value to a child in their knowing that there are some people who have a special interest in their welfare (ie, who love them)?
I wonder if the effect is stronger for people who don't have younger siblings. Maybe for people with younder siblings, part of the effect kicks in when they have a younger sibling (but they're generally too young to notice this), so the effect of becoming a parent is smaller.
I remember when my younger brother was born, and this sensation of going from this scaredy hypochondriac 6 year old (who worried about poisonous spiders, house fires, earthquakes, etc), to a mindset of "Okay, but what will I DO if there is a fire. How will I get me and little brother out the window?". There was this really sharp sensation of "Oh, I'm responsible now." and an associated values system shift, which... I suspect is similar to what a lot of people are talking about here?
Pretty much all of my adult life, my baseline levels of "protection towards children" are pretty damn high... to the point where I stand up and move to a more protective position when I see children near ledges, (even random strangers kids).
Of course... I don't yet have children of my own, so is hard to compare to what other people are describing with respect to having kids, but based on my own personal experience so far... yeah, I'd say younger siblings definitely CAN have a similar trigger effect.
Personally, while I like my younger siblings a lot (1.5y and 4y younger) I don't think I had much of this sort of effect. I didn't feel fiercely protective of them, media involving harm to children didn't bother me until I had my own kids, etc.
The transition to parenthood wasn't very pronouncd fir me - probably because I loved being around children before. Maybe you are onto something: I am the oldest sibling and I remember really liking to care of my twin siblings when the were babies and I was thirteen. I think it bit only prepared me but might also have kicked in the drive. I also remember studies showing that teens who have to take care of crying baby dolls as a means to discourag teen pregnancies didn't work too well because the girls developed affections for the baby dolls anyway. Maybe an experiment people could do is to find a family with kids and help out when their baby is small and see how it is. Also: Maybe people in rationalist group houses mit Kids could be polled?
Before I became a parent I cared about children in general, intellectually, in the same way that I care about people in general: a general sense that I want good things to happen to them. Over the first few days of Lily's life, however, I noticed I cared for her deeply and emotionally, where her wellbeing was incredibly important to me, and she was far more cuddly and interesting than I expected. Over the next few months, I realized that my disposition toward children in general had also changed, and while I didn't feel as strongly as toward my own, they were now similarly far more fun, interesting, and precious than they had been. I also started having strong emotional reactions to reading about harm to children. Paul Graham writes about a similar experience, though I think one a bit more sudden than my own:
Partly, and I won't deny it, this is because of serious chemical changes that happened almost instantly when our first child was born. It was like someone flipped a switch. I suddenly felt protective not just toward our child, but toward all children.
And Maia commenting on a post of Julia's:
For me it was like a switch flipped when I gave birth. The mental change felt similar to the mental change I went through during puberty: just adding a completely new biological drive I didn't have before. I actually didn't find babies very cute or interesting at all before, but I found my baby extremely so immediately
In deciding to have kids this is a very difficult factor to consider, because it doesn't happen to everyone. I have a vague impression that it is a bit more common in men than women, perhaps because women understandably have a higher threshold for deciding to have kids, but there are definitely men who expect it to happen and are dismayed when it doesn't and women who are surprised at how much their feelings toward children change.
Getting better at predicting this transformation seems valuable: since becoming a parent is a lifelong decision, the value of information is really high. Do people tend to have similar experiences to their own parents? Is it correlated with any other aspects of personality? Can your friends or other people who know you well predict this? Can it be triggered, if it's going to, by something less permanent than becoming a parent or is the permanence a key component? Is it something that may or may not happen, and when it happens it is a similar magnitude for everyone, or is it something where most people change a bit on becoming a parent, anywhere along a range from "imperceptibly" to "enormously"? Do we know how prevalent these changes are?