ומל ה' אלקיך את לבבך ואת לבב זרעך לאהבה את ה' אלקיך בכל לבבך ובכל נפשך למען חייך ... (ל-ו)
Chazal teach us that the first letter of the four words "את לבבך ואת לבב זרעך" spell out the word "אלול". The question is: Just because you do teshuvah, how and why does that effect a transformation in "זרעך" - your children?
Another famous remez for Elul is the posuk "אני לדודי ודודי לי". I am to Hashem, and He is to me. The Gemara in Kiddushin says that there are three partners in a person - the father, the mother, and Hashem. It’s fair to say that the more these partners function as a cohesive unit, the greater the positive impact on their charges will be. Thus, to the degree that it’s אני לדודי and דודי לי, the לבב זרעך will be affected too.
Another thought can be as follows: This parsha would seem to indicate a תשובה מאהבה, a teshuvah born of a love of Hashem, not due to fear of Him. If one repents out of fear, their children may not subscribe to it. If, however, they see the enthusiasm and love for Hashem and His mitzvos that their parents demonstrate, they’ll realize how lucky they are, and how special it is to be a Yid. As a result it won’t just be לבבך, but לבב זרעך as well, B’ezras Hashem.
R’ Yehoshua Leib Diskin zt”l explains the connection to the next posuk. The Torah tells us, "ונתן ה' אלקיך את כל האלות האלה על איביך ועל שנאיך אשר רדפוך". Hashem will place these very curses upon those who hounded you. He explains that Hashem forces himself to punish us in order to steer us toward repentance. If we do תשובה מאהבה, the זדונות then become זכויות, and the pain we endured at the hands of the Goyim was retroactively undeserved. Hence, Hashem will take these klalos we received and punish them with it instead.
May we have the siyata d’shmaya to do the proper teshuvah, enabling our next generation to grow closer to Hashem too, as our merciless opponents are swiftly punished for their actions by our merciful Father.