Some speculation

I'm not saying that's necessarily and always the case, but I think it's easy to overlook this possibility. (And then you also have parents who have difficulty asserting their authority with the child, and granted yes there are children who are innately more "troublesome" than others.) In either way, evil is not a word I would use myself for young children and infants.

The obvious other side of that coin is personal to me. My parents were cruel and abusive people with some serious issues.
None of us four children are rotten eggs and our personalities were not bent or shaped into something bad because of the beatings, starving us, or the mental and emotional torture they put us through. This included harsh bullying, criticizing emotion, gaslighting, and constant demeaning. 
It had some different, longer lasting effects, but it had nothing to do with our core personality or our action / reaction to life and other people, other children. 
All of us children are inherently kind and caring people. I am the only one that is assertive from the four of us.

There is only so much about the nature / nurture argument that can be true. 
You take a bad egg, and mistreat it, it will usually become worse. 
You take a good egg and mistreat it, and it sometimes goes bad. 
Those certainly exist.

There is a difference in the type of thing we are talking about.

For me, bad eggs can't be fixed, they are set from birth and are obvious as children. 
You woulld have to see what I mean when I say that if you try to manage them, they simply find other ways of being rotten, no matter what.

They are evil to me, there is nothing that is going to fix them or change them, and these didn't erupt from some momentary mistreatment or parenting scenario.

Certainly, there are those who do become something bad because of some treatment or personal biochemistry situation.
But that wasn't the type I am talking about. Where there, it is certainly possible to misjudge some of them at first glance. The daycare scenario is usually a longer term situation, where you spend more active waking time with these children than the parents. So passing this judgement doesn't come lightly, it comes from years of observation.
My sister was thinking about writing a book about it, mainly directed to the parents of these children. A "You haven't done anything wrong" type of book.

[Laird]

Yep, some stuff I've read previously plausibly affirms that some psychopaths are born, not bred. I can't seem to find it right now. If I do, I'll try to remember to share it here.

[Laird]

And almost immediately after posting, I found it:

When Your Child Is a Psychopath, in a June 2017 issue of The Atlantic, by Barbara Bradley Hagerty.

But even at a very young age, Samantha had a mean streak. When she was about 20 months old, living with foster parents in Texas, she clashed with a boy in day care. The caretaker soothed them both; problem solved. Later that day Samantha, who was already potty trained, walked over to where the boy was playing, pulled down her pants, and peed on him. “She knew exactly what she was doing,” Jen says. “There was an ability to wait until an opportune moment to exact her revenge on someone.”

When Samantha got a little older, she would pinch, trip, or push her siblings and smile if they cried. She would break into her sister’s piggy bank and rip up all the bills. Once, when Samantha was 5, Jen scolded her for being mean to one of her siblings. Samantha walked upstairs to her parents’ bathroom and washed her mother’s contact lenses down the drain. “Her behavior wasn’t impulsive,” Jen says. “It was very thoughtful, premeditated.”

One bitter December day in 2011, Jen was driving the children along a winding road near their home. Samantha had just turned 6. Suddenly Jen heard screaming from the back seat, and when she looked in the mirror, she saw Samantha with her hands around the throat of her 2-year-old sister, who was trapped in her car seat. Jen separated them, and once they were home, she pulled Samantha aside.

“What were you doing?,” Jen asked.

“I was trying to choke her,” Samantha said.

“You realize that would have killed her? She would not have been able to breathe. She would have died.”

“I know.”

“What about the rest of us?”

“I want to kill all of you.”

Samantha later showed Jen her sketches, and Jen watched in horror as her daughter demonstrated how to strangle or suffocate her stuffed animals. “I was so terrified,” Jen says. “I felt like I had lost control.”

And almost immediately after posting, I found it:

When Your Child Is a Psychopath, in a June 2017 issue of The Atlantic, by Barbara Bradley Hagerty.

Without presuming guilt I do have to wonder if this child experienced abuse - not necessarily the parents.

Among my younger cousins I had one that was two and one that was just 6 months old, and the older one did try to choke the baby.

Years later they are both quite well adjusted, married with kids, and have no memory of those events.

edit: I also wonder if this lack of treatment options is due to the materialist faith dominating academia...

[Laird]

Without presuming guilt I do have to wonder if this child experienced abuse - not necessarily the parents.

Though your sentiments are understandable, I'd recommend reading the article in full. Here are some quotes from further down (you might not find them convincing, but the article as a whole is, at least to me, convincing):

Researchers believe that two paths can lead to psychopathy: one dominated by nature, the other by nurture. For some children, their environment—growing up in poverty, living with abusive parents, fending for themselves in dangerous neighborhoods—can turn them violent and coldhearted. These kids aren’t born callous and unemotional; many experts suggest that if they’re given a reprieve from their environment, they can be pulled back from psychopathy’s edge.

But other children display callous and unemotional traits even though they are raised by loving parents in safe neighborhoods. Large studies in the United Kingdom and elsewhere have found that this early-onset condition is highly hereditary, hardwired in the brain—and especially difficult to treat. “We’d like to think a mother and father’s love can turn everything around,” Raine says. “But there are times where parents are doing the very best they can, but the kid—even from the get-go—is just a bad kid.”

Still, researchers stress that a callous child—even one who was born that way—is not automatically destined for psychopathy. By some estimates, four out of five children with these traits do not grow up to be psychopaths. The mystery—the one everyone is trying to solve—is why some of these children develop into normal adults while others end up on death row.

Though your sentiments are understandable, I'd recommend reading the article in full. Here are some quotes from further down (you might not find them convincing, but the article as a whole is, at least to me, convincing):

Ref: 4 out of 5, where one is the actual psychopath. That is one psychopath too many.
I assume, if you followed the other 4, other difficult situations likely erupt if they are borderline or rotten at some core level. Or they become politicians, bosses, CEO types, lol. Sorry, can't help but point out the obvious.
It takes a certain callous approach with total avoidance of any sympathy to survive in most societies. Otherwise people get abused and mistreated by those who are that callous. People live in a mostly anti-social bubble of make-believe stability, while feigning social interests or concerns.
Where, to bring this back to reincarnation, why can't rotten people be born rotten over and over?
If the core is rotten, and nothing was learned or changed in the last life, they just continue on the same trajectory.
I usually smirk to myself when people assume that the "higher self" is always somehow this highly advanced, loving, caring being.
I personally just don't think so. The trend has always been that the mob is a dangerous and unstable crowd of hateful beings that will torture and burn, while foaming at the mouth, exclaiming they are somehow more advanced, better than, or some other elite herd intoxicated separate group from those they torture.
The main reason for many wars has been fundamentalist brainwashing, us and them, they are ALL evil, we are chosen, etc.
It also underlines that it could be very possible that some of the people here are imprisoned criminals, trapped in bodies to learn or be punished.
It doesn't mean everyone on the planet is a criminal from some other galaxy, but it could.

Though your sentiments are understandable, I'd recommend reading the article in full. Here are some quotes from further down (you might not find them convincing, but the article as a whole is, at least to me, convincing):

Hard wired in the brain? Does this mean they've isolated the parts of the brain that cause psychopathy, or they are leaning on assumptions of their materialist faith?

I know the article mentions all sorts of brain-mind connections but it seems somewhat presumptuous to me.

(I actually recall reading this article when it came out, but will give it a re-read as I probably forgot many things.)

Hard wired in the brain? Does this mean they've isolated the parts of the brain that cause psychopathy, or they are leaning on assumptions of their materialist faith?

I know the article mentions all sorts of brain-mind connections but it seems somewhat presumptuous to me.

(I actually recall reading this article when it came out, but will give it a re-read as I probably forgot many things.)

The brain is very plastic and constantly updating connections, creating new ones, ever changing.

However, what I know (by digging into way too many brain studies) is that what we diagnose as sociopath or psychopath using symptoms or behavior, can often be seen in brain scans. It has a "signature' brain structure and frequency patters, very particular neural networks, and likely very particular chemistry.

So the quick and easy answer is yes, they have isolated brain structures and neural networks that are directly related to these issues.

We can see all sorts of other very standard neural networks and very easily see emotions, or general thoughts that are similar creating the same neural patterns. We see the handshakes necessary between various parts of the brain to speak, listen, type, or think about doing these things, etc.

One of the very funny scenarios was when one of the brain research scientists scanned himself as a control for an experiment, and this scan identified him as either a sociopath or psychopath, I don't remember which. But... go figure, he has none of the symptoms or behavior.

So, it would be wrong to scan children and make assumptions, or the public for that matter. But scanning people can certainly help diagnostics, or point in the correct direction.

This pointed me in the direction of thought that this condition had to include something deeper than just the brain scan and resulting configuration.

To return to the original idea, that children being incarnated might include improved skills because they don't have to relearn, or they learn old skills faster, etc.

It happens, is rather random, and it is not always the same skills that surface. One can sew, one can fish, one can fix engines, one knows another language. No consistency or constant there.

There was always the attempt to try and match any known previous life information with this skill, which was not always possible, and as they stated, we don't know if it was carried forward from another life before the memory in question, or the life before, etc.

We also have brain damage induced savants. People who were never musical and are suddenly able to play instruments like a pro, or speak another language, or paint / draw. Did the brain damage release a past life skill or memory? If so, why was it being blocked in the first place? Anything helpful should be surfacing on demand. This is a world where these things would be a helpful advantage. Either suppression is part of some punishment, learning experience, or it just doesn't work that way.

Any form of brain illness like dementia, and many drug induced problems, will convince you that there are no strict unified answers to anything about memory, personality, or the brain.

Though your sentiments are understandable, I'd recommend reading the article in full. Here are some quotes from further down (you might not find them convincing, but the article as a whole is, at least to me, convincing):

"But other children display callous and unemotional traits even though they are raised by loving parents in safe neighborhoods. Large studies in the United Kingdom and elsewhere have found that this early-onset condition is highly hereditary, hardwired in the brain—and especially difficult to treat. “We’d like to think a mother and father’s love can turn everything around,” Raine says. “But there are times where parents are doing the very best they can, but the kid—even from the get-go—is just a bad kid.”"

By "hereditary" I assume that means one or possibly both parents are known psychopaths. Yet these same parents were also "loving"?