In small children that bratty/spoiled "asshole" behavior is learned from parental inconsistency and reinforcement of negative behaviors. That has been proven over and over again.
This is what I was referring to.
A young child since the topic was spanking.
Because once you get into those older children... really?
Once you get to puberty and into young adulthood things get more complicated re development.
The outside world and peer groups play a much larger role in character development at this point and can have a huge impact during the survey period. As can perceived traumas... that are specific to the individuals temperament such as fighting in the home between parents (for instance one child my internalize the fighting while the other may not, and indeed may not see the parental fighting as an issue that affected them at all). During all of this of course the foundational character that was developed during early childhood is important, if the child feels like there are strong bonds this is better, and perceived fear or distrust creates more instability where family is concerned.