Can you please clarify why exactly women and children are not included? Or rather, what exactly this phrase means and perhaps the reason behind it.

Referring to the translation aforementioned, the translator has not been accurate enough, since the sentence referred to in your email should read: “O Allah forgive so and so, mentioning the name of the believing men in place of so and so.” In general there are many issues that we do not know the reason for the way they are. For example we do not know the reason for the Salaat-al-Fajr being two Rak’ah, and not three or four, etc. And the reason for mentioning the men in the Qunut of Salaat-al-Witr could be of such category. However, when it is said that forty men should be mentioned in the Qunut, it does not mean exclude the women and children, but in fact to include them, since men are considered as the head of the family and to represent them. Therefore when a man is mentioned in the prayers it is intended to include that man as well as his family, i.e. the idea is to pray for forty family, each of which is referred to by the head, or representative of that family. Furthermore, one may also pray for women and children, provided you mention the minimum number of (40) men.