Which group is not included in the Birth Order theory?

The Birth Order theory, developed by psychologist Alfred Adler, posits that an individual's personality and behavior are influenced by their position in the family structure. This theory identifies the dynamics and characteristics often associated with various birth positions—specifically, firstborns, lastborns, and only children are commonly discussed.

Firstborn children are typically described as responsible, achievement-oriented, and often have leadership qualities. Lastborn children are often characterized as more free-spirited, social, and sometimes more dependent. Only children tend to exhibit traits associated with firstborns due to their singular experience of seeking parental attention and often being more mature for their age.

The second child does not have a well-defined role in the Birth Order theory. Unlike firstborns or lastborns, the second child is more often compared to siblings and can fall into different patterns depending on the family dynamics at play, making it challenging to categorize them distinctly in the same way as the other groups. As such, the theory does not explicitly include a set characterization for the second child, leading to it not being recognized as one of the primary groups in this context.