There were three children in my family. Me, being the oldest, a sister, and a younger brother. We were a tight group, due to traveling the world with our military father. Essentially, since we had no extended family nearby, we had to fend for ourselves for play, sharing, interaction with non-family, emotional support and the absence of our father because of his duties.
I can look back now and see some advantages and disadvantages having siblings.
We kept each other entertained if there were no friends available. This may seem like a rarity to most, but during the post-World War II rebuilding of Germany in the 1950s, we lived on the local economy and did not always have access to other English speaking children, so we made friends and played with the locals. A side advantage of this was that my sister and I were able to pick up a sufficient mastery of the German language to get along.
With siblings there is the issue of sharing resources. This could be toys, or in the case of limited space in our living quarters, my brother and I might share a bedroom. Each of us had our individual demands on our parents’ time as well.
Emotional support was important for the long periods of time that we would be half a world away from other family members such as grandparents. This was compounded if our father was away on duty for an extended absence.
In retrospect, I see the positives of having siblings. We learned to share. We comforted each other when needed. We played as well as siblings of differing ages could. We dealt with the absence of a parent or other relatives by engaging with non-family, even those of a different culture.
I was an only child for three years; not enough time to develop traits specific to an only child.
With an only child of our own, my wife and I have found that raising one child is more difficult than raising siblings. One child requires all of your attention. You do not have the luxury of siblings entertaining themselves. But one child allows you to direct all your attention and resources to the child. There is no competition for resources whether it is fiscal or emotional. One child gets it all. However, with one child, if mistakes are made, there is no second chance.