Only children always want to get their way, can’t share and are generally selfish—or so the long-held prejudice goes. According to recent research, however, these claims are overstated. So where did these biases come from?

from https://www.scientificamerican.com/article/is-only-child-syndrome-real/
https://static.scientificamerican.com/sciam/cache/file/71A0851D-906D-4F5E-AF6F44F5D62FF763_source.jpg?w=590&h=800&6311B9F0-6C0C-4484-8F20955CF86FBEF6