This has gotten me wondering what subjects do you broach in letters to your parents? I have only written a few letters to my mother and in no way did I broach the subject of intimate relations or even periods. My mother's eyes aren't fully wonderful nor are here hands thrilled to have arthritis, so reading and writing letters isn't easy for her. Do people still write to their parents? My mother has a habit of telephoning when I am in the bathroom or up to my elbows in washing up water. Telephones need both parties to be available at the same time - that's why I like letters, because you both read/write in your own time. E-mail is an option but for my mother, she isn't interested in the technology these days. I barely read/write emails myself these days. So, for her, it is the telephone that connects us but we don't speak about those taboo subjects.
Edit - I have now finished the book and I thoroughly enjoyed it. A bit of one letter especially made me laugh:
There is a large bridge near my house, which was designed by Theodore Roosevelt, and on each corner there is an enormous bronze statue of a bison. Now someone has painted the prominent personal organs of these bison bright red, so that everyone who crosses the bridge stops and roars with laughter. It is a very fine sight and I don't know who's going to take the paint off. You can't really have a fireman or someone leaning a ladder against the animal, ascending it and solemnly scraping the paint off the penises. A crowd would gather and laugh at him, and photographers from a bawdy newspaper would get a wonderful photograph.