A woman in her early forties was talking to me about how her parents still thought of her as the baby of the family and a bit "flaky" a description that does not match what I know of her. But, they might consider me "flaky" too.
She also was unhappy how they listened to her brother and gave him credence and not her, even when he was wrong and she was right.
As a mother of one child I didn't have to worry about showing favoritism. I could be as bonkers about her as I wanted without having the accusation that I loved her best.
Not showing preference and being fair is something that must be difficult, especially when children (little or adults) have different personalities and different needs.
I so admire another friend with two grown sons who are so different in personality and needs that if I didn't know better I would think they came from different sets of parents if not different species. She sweats making sure that both are treated fairly. If she were to treat them identically, one of the other would be unhappy, but she resorts to balancing values and doing what they need from her.
Siblings also see slights, some intended, some not.
Even though my mother died 25 years ago, I've gone from resentment to annoyance that when my mother had my brother and I to dinner at the same time, she could carry a six-pack of beer up the stairs for him, but my liter bottle of Coca-cola was too heavy. I resisted taking out a scale to prove her wrong.
Some kids are born into the wrong families. An artistic child might not be understood by accounting parents or vice versa.
Although I believe 99.9% of parents want to do the right thing by their children, never will any on-the-job training be so difficult.
By the time we learn, the kid is on his own and probably complaining that we didn't do this or that right...they would be correct.