While I realize I'm a little late to the party on this one, what I have to say needs to be said.
The fact that, as a society, we teach our children that only infants and toddlers need to wear diapers and/or that wearing [a diaper] after a certain age or point in our lives is wrong. Such teachings are not only misleading, but detrimental to the emotional and social progression of individuals such as this child.
In no way do I advocate *or support* any form of paraphilic infantilism (I suggest getting psychological help for this issue), but we have to stop belittling our children when they exhibit behaviour(s) we don't expect or understand.
To the trolls who've posted here: please go away - and get some help.
You might want to google it. It's called Diaper Fetishism. If you were to say your 5 year old grandson wasn't fully potty trained yet, or had frequent accidents, that's a completely other thing. Obsession with diaper wearing is probably not likely to go away with time.
You say that he is five. A lot Happens, when you are five, you start Big School- no small 'thing' for a child. He may, very well, not say so but.....he could, in all probability, be Terrified! Can you blame him for seeking Comfort, in Lovely Warm, pants- especially when it's So Easy to achieve.
My advice, would be, Talk to him- not at a Stressful time- maybe read him a story and just gently ask him why he Wets himself- His answer might surprise you! A friend of mine, asked his Daughter, why she Pood herself at the Gym. Her answer was simple, she didn't like the Sound of the water Dripping and therefore didn't use the toilets. (You might ask 'why there were no Wet Accidents'....There were, in the pool) A simple answer was Found, Mummy simply accompanied the girl.
Please do, bare in mind, that wetting/Messing is often seen as a Problem to the Parents- not necessarily the child. Johnny/Jenny might actually not mind, at all, being wet, or messy- it's not harming then after all.
As I said above, find a 'Good' time to talk to your child. The answer might be staring you 'in the face'. Good Luck.
AndrewDavid1
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.