Size 7 Luvs diapers will fit an 8 year old boy as long as he's average weight.
If your 8 year old boy is not overweight then he should easily fit into a size 7 Luvs diaper or other brands of size 7 diapers.
They also make a size 8 diaper in Pampers Swaddlers and even Huggies now that can easily fit an 8 year old boy.
The size 7 diapers are made to fit kids up to 60 lbs of weight.
The average weight for an 8 year old boy is 56 lbs so the size 7 Luvs diapers should easily fit your 8 year old boy.
Some 8 year old boys may only weigh 50 lbs which is also healthy.
I have autistic 8 year old boy that is wearing Luvs size 7 diapers full time because he is not toilet trained yet and he may or may not ever be toilet trained.
He loves the Bluey designs and gets excited about them.
If he outgrows the size 7 Luvs diapers then I will likely switch him to Huggies size 8 snug and dry.
After size 8 you can buy Youth Diapers as well.
If your 8 year old son will wear the Luvs diapers then I recommend them.
Dollar General also sells Gentle Steps size 7 diapers that will fit an 8 year old boy.
Luvs diapers, Huggies diapers, Gentle Steps diapers and other tape on diapers would be much better for bed wetting than Goodnites are and they are cheaper and hold more.