Kekkei Genkai are hereditary abilities that allows the users to special techniques.
Even though they are genetically inherited, we only know the names of a strikingly low number of (living) young users for each clan in the original run of Naruto anime series.
For example, we only see Haku as the user of Ice Release, Kimamaro as the user of Shikotsumyaku, Sakon and Ukon as the user of their unnamed Kekkei Genkai.
Even for well known clans, there is only Sasuke and Itachi, the wielders of Sharingan, from the Uchiha clan (granted, it was due to Itachi wiping them out); and only Neji and Hinata, the users of Byakugan, from the Hyuga clan.
Correction
Um actually ... there is actually also Hinabi, Hinata's younger sister, from the Hyuga clan.