Regarding the question whether or not Kaoru was really the son of Kashiwagi, it seems to be true that Hikaru Genji and Yugiri (Genji Monogatari) felt that his eyes were similar when they saw Kaoru as a small boy ('Kashiwagi,' 'Yokobue') and it was repeatedly described that, while Genji's lineage including Emperor Reizei were good at painting ('Eawase'), the To no Chujo's lineage including Kashiwagi were good at music, and Kaoru played the koto and flute, which Kashiwagi was also good at this shows him to be close to the lineage of To no Chujo ('Takekawa,' 'Yadorigi').
薫が本当に柏木の子であるかどうかについては、光源氏や夕霧(源氏物語)が幼い薫を見て目元が似ていると感じており（「柏木」「横笛」）、また冷泉帝ら光源氏の血筋は絵画（「絵合」）、柏木ら頭中将の血筋は音楽に秀でているといった描写が常々なされているのに対し、薫は柏木が得意とした琴や、横笛を演奏して頭中将の血筋に近いとされている（「竹河」「宿木」）ことから、間違いないようである。