In others, it is the longing to be literally back in diapers.

In still others, it is the delightful humiliation
of being just a "Big Baby."

Yet others have more of a fetish, a sexual attraction
for diapers or other infantile objects.

Infantilism is a set of variations with a common  theme:
Diapers and Babyhood.

Typically, an infantilist realizes he is different between the ages of five and fifteen.
He realizes that he has a strong desire that most people do not share.
Generally, these desires are hidden, kept as a dark secret. He feels that only
he, out of all humanity, is like this.

It is nearly harmless in and of itself, but he still represses it.
He fears disgrace, ridicule as a pervert or a weirdo.
He fears being abnormal.

To make matters worse, there is also the stigma of pedophilia.
Equating pedophilia and infantilism is common, but not correct.
Pedophiles involve (abuse) children, while infantilists become
children themselves.

It makes as much sense to equate transvestitism
(men who love wearing women's dresses)
with male heterosexuality (men who love women).

One deals with how a person sees himself (subject)
while the other deals with what that person is looking for in someone else
(object). Infantilism is a paraphilia. Paraphiliasare unusual desires that people have.
More common examples include masochism and rubber fetishes.

Typically, these are focused, deep longings.
They are often  life-long. As evidence to the persistence
of these urges, many who have them struggle desperately against
them for years or decades, and very few, if any, can claim
to become free of them.

Hopefully, eventually, there comes a time when the isolation is broken.
The infantilist finds out that he is not alone. Perhaps he sees something
on TV, or finds something on the Internet. The urges remain,
but he is now free from the solitude.

Perhaps you are here because you have recently found -
with a joy that warms the soul that you are not alone.

Perhaps you are here because someone has trusted you
with their deepest secret - that they like diapers.
Either way, you have a lot of questions that need answering.
This is a good place to start.