A 5 year old can wear Luvs size 6 diapers.
If the 5 year old is skinny enough and average weight and not overweight then the Luvs size 6 diaper should fit the 5 year old boy just fine.
I have a 5 year old boy that wears Luvs size 6 diapers because he's not potty trained yet.
He wears the Luvs size 6 diapers day and night and they fit him just fine.
His 7 year old brother also wears Luvs size 6 diapers as well for bed wetting and when away from home.
The Luvs size 6 diapers fir the 5 year old boy and the 7 year old boy just fine.
I'm sure they'll both still fit in the Luvs size 6 diapers even when they are 8 and 10 years old because they are really built skinny.
However if your kid is bigger then they would need a size 7 diaper or a Youth diaper.
But for most skinny sized kids a Luvs size 6 or even size 7 diaper should easily fit them.