Size 7 diapers will fit an 8 year old boy as size 7 diapers fit kids 41 lbs and up and even a size 8 Pampers Swaddlers will also fit an 8 year old boy.
If your 8 year old son is wetting his pants daily then you should put him back in diapers full time.
I would also like you said treat him like a baby, give him a bottle, pacifier, crib etc.
Also when at home keep your 8 year old son just in his diaper and shirt like Tommy diaper boy in the pictures below and make him use the diapers for both poop and pee.
Your 8 year old son will learn to love his diapers if he doesn't already.
