Megillas Esther ends by saying: וְדֹבֵר שָׁלוֹם לְכָל־זַרְעוֹ - and speaking peace to all his seed.
I realize Rashi applies this to the previous clause, of all the nation, but perhaps there are interpretations that are not in accordance with this.
Did Mordechai have children? With whom? What information, if any, is available about them?
Megilla 13b says that Ester would "rise from the bosom of Achashverosh and immerse herself and sit in the bosom of Mordechai". Tosfos Harosh asks how this was permitted due to the law of "havchana" (the requirement for a women to abstain from relations for three months between husbands to identify the father), and explains that she utilized anti-contraceptive techniques to avert the problem. He then asks if so, how was Koresh born, and (according to one answer) explains that Koresh was in fact Mordechai's biological son, and was only referred to as Achashverosh'es son because he grew up in his house.
Chazal say (and the medrash brings this pasuk as a proof) that a person's students can be considered like his children. Thus וְדֹבֵר שָׁלוֹם לְכָל־זַרְעוֹ is referring to his students who are viewed as his children.
If you want to discount Rashi you can simply say that זַרְעוֹ refers to Mordechai's descendants through Esther (whom the Megillah calls his daughter). She had a son, Daryavesh who would be Mordechai's grandson.