The rav answered yes—use dry wine rather than sweet for Havdalah.
So they started making Havdalah over dry wine.
Then with a beaming smile, my friend said, "And our fourth was a girl!"
The Mystery of the Segulah that Seemed Not to Work
No idea. I made that up. (And anyway, boys can also be sweet—I mean, at least when they're not bringing home mud, ripped pants, scratches, bruises, or scorpions, and the like...)
Anyway, a father of boys went to Rav Kanievsky to elicit a blessing for a daughter, and Rav Kanievsky recommended the above segulah.
After 2 years, the man returned to Rav Kanievsky to report that since then, Hashem continues to bless them with sons, not daughters.
"Yayin nesech," replied Rav Kanievsky—wine handled improperly, making it halachically prohibited for drinking.
The answer startled the father because he & his family were very frum people committed to Jewish Law.
However, they frequently made Havdalah at the home of his wife's father.
So this father of boys contacted his father-in-law to ask about the handling of the wine used for Havdalah and discovered that, indeed, this father of boys had unknowingly been using yayin nesach for Havdalah.
Hopefully, with their newfound knowledge (and newly bought & guarded dry wine), they'll be making a kiddush rather than a brit milah in the upcoming future!