I do think it depends on the personality and temperament of the child, and their placement in birth order can also have some influence. That being said, I raised a boy (1st born), and 2 girls (the youngest being adopted). My son was the picture perfect child. Always well behaved, well mannered, content, protective of his mother and sisters, obedient, helpful, good student, hardworking, goes with the flow, kind, loving, generous, caring. This is common with 1st borns, eager to please. My 2nd is also typical of her birth order. Daring, challenging, often a handfull, somewhat self centered or self aware, risk taker, outspoken, can be hot tempered (gets this from her dad), hates to lose, independent. My 3rd was always so private it was hard to figure her out or know what was going on in her head. She was fun loving, loved jokes, brought together and united a unique group of friends of 3 races, excellent student, but hated to work, independent. In my case, the boy was by far the easiest....but was it because he was first born? Was it because he was the only boy and felt he needed to be gentle for the girls? He was quick to start walking and to potty train, but slow to talk and read. The girls were MUCH harder, the older one was quick to argue with parents and rules, always trying something, or into something, sneaking out, taking chances, etc. She was very early at talking, very late to walk and potty train, struggled with school. The youngest was so private, when we learned something about her it was always a surprise. Despite her fun side, and love of jokes and laughter, she struggled quietly with depression. She was average in developement be very smart and talented. Hard to say how/why each was so different, except that God creates each one of us to be unique.
On the other hand, my late husband was the oldest of 3 boys. Through childhood and well into adulthood, they were all a challenge, fighting constantly (I'm talking punches and more), disobedient, sneaky, risk taking, rowdy, girl chasers, lieing, stealing, etc. I swear....there's NO way I could have raised those three boys. I think I would have run away and changed my identity.