If I had an 8 year old son and he came home with poop in his pants I would get him cleaned up and put a nice thick diaper on him.
He would then be wearing diapers for the rest of the year and would go to school wearing a thick diaper as well.
I would then go to his school and change his diapers for him when needed.
He would have to pee and poop in the diapers and at home he would be wearing nothing but the diaper or just the diaper, shirt and socks.
I'd also make him drink from a baby bottle, sleep in a crib, suck on a pacifier and I'd treat him as a little toddler in diapers.