From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Only_child
 
An only child is a person with no siblings, biological nor adopted.

Children who have half-siblings or step-siblings, either living at the same house or a different house - especially those who were born considerably later - may have a similar family environment to only children, as may children who have much younger siblings from both of the same parents (generally ten or more years).
 

Overview