Why do older children like wearing nappies and plastic pants?

There can be many reasons for it. He may have more difficultly realizing he needs to pee (Congenital insensitivity to pain with anhidrosis) or other organ dysfunction and muscle tension issues. So he is afraid he may not make it to the bathroom and wet himself. Some people may also simply prefer them, or have had issues regarding using the toilet and have found that wearing diapers is preferable.

If none of these things are the case, then he might have infantilism, a diaper fetish, some other condition, or might simply want to wear diapers and/or be a baby. Most doctors consider it harmless, but undesirable. If you need more information on this, I suggest understanding.infantilism.org/