This is a sexual fetish which is all about role plays where a person returns to infancy.
There are two main types. There are the general adult babies and there are the sissy babies. The latter are male fetishists who typically wear female infant clothes. Both like to wear diapers.
There are also diaper lovers who do not act as infants at all. These fetishists are more attracted to the humiliating aspect of being forced to wear a diaper and made fun of.
There are two main types of role plays for the adult babies and sissy babies. One type is humiliating and masochistic. They may get punished for having wet or dirtied their diaper. The second type of infantilists love a more nurturing, a more gentle ritual where they can forget about their adult responsibilities or enjoy someone pampering and caring for them. They desire a parent-baby role play where they are being washed, they drink from a baby bottle, are being changed into diapers, taken to a crib for their “nap time” and some may even simulate lactation.
There is a big ABDL (Adult Baby Diaper Lover) community. Online there is a special app for Autonepiophilia lovers looking for an adult diaper date or to expand their social network within this fetish community. ADBL parties and other related events are organised all around the world.