>>42756 (OP)
If your brother wears multiple diapers, always make it a point to pluralize the word diapers. Refer to your brother’s diapers as his diapers as much as possible. Use the possessive form of his name whenever you can, or at least say “his diapers” when it is understood that you are referring to the diapers that he wears. Avoid generic references to his diapers if the context of your statement allows you to specify that the diapers belong to him. At the same time, avoid referring to any pants that he might wear as “his pants”. Even though the pants may actually belong to him, care should be taken to avoid mentioning that he has any pants to call his own along with the diapers that most definitely are his. You should refer to your brother and all diaper-wearing boys as “boys”, or better yet, “diaper boys”. Other non-diaper-wearing “boys”, such as your classmates, boys you might have crushes on or are friends with or dating, should be called “guys” instead. Whenever possible, use the word “diaper” to modify relevant nouns. For example, always call them “diaper pins”; don’t just call them pins. Always call plastic pants “plastic pants.” Never, ever should they ever be called “panties”! In Deekerian parlance, “panties” are Girls’ underwear. When your brother is writing about you as his Diaper-Changing Sister, insist that he always capitalize common-noun references to you, as exemplified in this sentence. To him you are his Sister and you are a Girl when it comes to his diapers.
Penis: There are dozens of synonyms for a boy’s genitalia, some of which are purely sexual in nature (e.g. “cock”) so these should be avoided. You can’t really go wrong with referring to his penis as “his penis”. There are a few other juvenilely acceptable terms such as “pee-pee”, “wee-wee” and “wiener” that you can probably use. “Peter” is also marginally accepted, though it does seem to teeter towards having sexual connotations.
Testicles: A wide range of words have come into use to refer to a boy’s testicles. The most common are “balls” and “nuts”, though “nads” is often used, too. Most families should accept the use of “balls” and “nuts”, and their variants “ball sack/bag”, “nut sack/bag”. Other words such as “(family) jewels” and “cajones” are used mostly by teens and adults. Words such as “junk” and “package” generally refer to the penis/testicles collective and are also generally used by teens and adults, though not necessarily always in a sexual context.
Erections: Popular culture and its focus on sex have led to a colorful array of words to describe a sexually stimulated penis, which you will certainly see when you are changing your brother’s diapers, even if he is several years away from puberty. “Hard-on” is probably the most common noun form, but “stiffie” is also often used. These terms should be acceptable within most families, as would be the adjective counterparts “hard” and “stiff”.
Other sexual terms: In the context of performing a diaper change it isn’t likely that you would need to talk about your brother’s masturbation, ejaculation or other sexual activity, but in some situations surrounding diaper changes and his diapers in general, these matters are naturally bound to occur. Because this guide is not so much about a boy’s sexual response to his diapers as it is to the process of diapering him and acknowledging his diapered state, this is an area that I feel is best left to the discretion of the individual.