Diaper obsession

Why is my almost 5 yr. old grandson, seemingly all of a sudden become obsessed with wearing a diaper? He doesn't have a new baby sibling, and we have told him he is a big boy and only babies wear diapers. We have also given him a lot of positive reasons it's a lot more fun to be 5 yrs. Old than being a baby. He still wants to wear one. Any answers? HELP,  DISTRESSED.

[AnnieBrooke]

Try not to be distressed.  He might just like the way it feels, emotionally or physically (the thickness).  Let him wear pullups in an appropriate size.  Because they work just like underpants, he can still use the toilet the way he does when in underwear.  Let him wear them a while.  He'll doubtless change his mind about it soon enough.