“These are the children of Yitzchak ben Avraham. Avraham fathered Yitzchak” (Bereishis 25:19). The question is, after the Torah mentions that Yitzchak was ben Avraham, why does it need to say after that Avraham fathered Yitzchak? If I tell you Yitzchak is ben Avraham, most geniuses, even simple folks like me and you, could figure out that Avraham fathered Yitzchak.
In the Torah, we see statements or episodes that to the simple mind and eye might seem insignificant. The Torah tells us that Rivka, the wife of Yitzchak, finally becomes pregnant, and the Torah states, ויתרוצצו הבנים בקרבה – and the children struggled in her womb (Bereishis 25:22). Onkelos teitches (translates) this to mean ודחקין בניא – her children were pushing within her womb.