My advice on telling your parents that you want to wear diapers is to not actually tell them.
Your parents will likely get mad at you for wanting to wear diapers and once you tell your parents you want to wear diapers there's no going back.
Your parents will know about it for the rest of their lives.
I got caught wearing a diaper when I was 7 years old and was wearing my little brothers plastic backed Luvs diapers then.
He was 2 years old and I got into trouble for wearing the diaper.
My mom made me take it off and told me if it happened again that I would get a spanking and then be treated as a baby.
But it never happened.
She wasn't gonna treat me as a baby in a loving way anyway and it would really be awkward.
However if you really do want to tell your parents then you can send them a text, email or just tell them straight out that you want to wear diapers.
Or start wetting your pants or wetting the bed at night and then tell them that you want to wear diapers as protection in case you wet the bed again.
It's doubtful though that your parents will get you more diapers.
I would just save some money and go to a store such as Walmart or Dollar general and buy some Luvs diapers yourself.
You can buy small packs of Luvs diapers for around $5.00 which has 20 diapers in them.
The package of diapers can fit into a backpack easily.