What is only-child syndrome? Traits, causes, and whether it’s real by Hannah DeWitt | Jul 31, 2025 | Children, Teens, & Adolescents, Mental Health Topics, Parenting “Only-child syndrome” is a popular but controversial term used to describe a set of traits or characteristics thought to be common in children who grow up without siblings. These traits, often painted in a negative light, can include selfishness, loneliness, introversion, difficulty sharing, and an overdeveloped sense of independence. However,…