You should put your 6 year old potty trained boy in diapers for a road trip.
All kids even potty trained should wear diapers when on a road trip because it means they don't have to hold their pee in.
Wearing a diaper on a road trip even when potty trained saves the pain of having to hold the pee in while you look for or wait for a rest stop.
My kids wear diapers on road trips and I let them know it's okay to just use the diapers.
Then when the diapers get full and we're at a rest stop I change their diaper.
My kids wear Luvs size 6 diapers on road trips and they hold up good.
Sometimes they can go a few hours or so between diaper changes and they never even use the toilet on the road trips because the diapers are more convenient.
An 8 year old boy should be able to wear Luvs size 6 diapers.
Luvs size 6 diapers have pretty stretchy tabs that stretch quite a bit to fit.
Pampers baby dry size 6 may also fit the 8 year old boy or even size 7 pampers cruisers diapers or size 7 Gentle steps diapers.
If your 8 year old boy won't fit into the size 6 Luvs or other size toddler diapers then you can buy a Youth sized tape on disposable diaper online such as Attends Youth diapers.
A 7 year old boy can wear Luvs size 6 diapers if they are skinny enough.
If the 7 year old boy is an average size and skinny built then they should be able to easily fit into a size 6 Luvs diaper.
Luvs diapers have really stretchy tabs and they should easily fit a 7 year old boy.
If not then a size 7 Pampers Cruisers or Size 7 gentle steps diaper should easily fit the 7 year old boy.
A 5 year old boy can wear Luvs size 6 diapers for bed wetting.
The Luvs size 6 diapers have really stretchy tabs so they can easily fit most kids of 5 to 10 years old just fine.
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.