The 20-year-old model and 18-year-old reality star shared adorable new photos with the 1-year-old on Instagram. Reign Aston Disick is the youngest child of the Jenners' half-sister, Kourtney Kardashian, and her ex-partner, Scott Disick.
Kendall and Kylie are also aunts to 6-year-old Mason Disick, 3-year-old Penelope Disick and Kim Kardashian's children, 2-year-old North West and newborn Saint West. Kendall was mobbed by reporters asking about Saint upon her return to Los Angeles last week.
Kourtney and Scott were together nine years before splitting in July, and sparked reconciliation rumors by reuniting over Thanksgiving. The 36-year-old mom-of-three was linked to 21-year-old singer and family friend Justin Bieber over the weekend.