Why does the Torah list the sons of Amram, Yitzhar and Uziel, but not those of their brother Chevron? He had sons, for it says (Bamidbar 3:27) "u'Mishpachas ha'Chevroni"!
Moshav Zekenim: Amram, Yitzhar and Uziel, the Torah mentions children from theim 1 , but not from Chevron. Likewise, it does not name here the sons of Isamar (Rashbam) or Moshe (Hadar Zekenim), or the grandsons of Gershon and Merari (Da'as Zekenim, verse 21).
Da'as Zekenim (verse 21): He did not have sons. 2
Rashbam: E.g. Korach from Yitzhar, Misha'el and Eltzafan from Uzi'el. Even though the sons of Korach are named only here, they are mentioned elsewhere (u'Vnei Korach Lo Mesu - Bamidbar 26:11).
Why does the Torah tell how long Kehas lived?
Rashi: It teaches that the 400 years decreed at Bris Bein ha'Besarim were not all in Egypt, for Kehas descended to Egypt, and if we add all his years and Amram's and 80 of Moshe, we do not reach 400. Rather, they are counted from Yitzchak's birth.