Wiktionary
n. The act or process of infantilize, or treating a non-infant as an infant
Wikipedia
Infantilization is a term referring to the treatment of one who is not a biological child as though he or she is a child. When used in reference to teenagers or adolescents, the term typically suggests that teenagers and their potential are underestimated in modern society, and/or that adolescents are often regarded as though they are younger than their actual age.
People who are the subject of infantilization by others are said to have been "infantilized." Studies have shown that an individual, when infantilized, is overwhelmingly likely to feel disrespected. Such individuals may report a sense of transgression akin to dehumanization.
There can be an overlap between the terms "infantilization" and "patronization", although infantilization derives more specifically from a sense of age group or hierarchical seniority on the part of those responsible for infantilization.
Infantilization may also refer to a process when a child is being treated in a manner appropriate only for younger children.