Kendall Jenner Says Niece Stormi, 3, Has 'Biggest Crush' on Boyfriend Devin Booker

"I'm, like, jealous sometimes!" Kendall Jenner jokes of niece Stormi's "amazing" friendship with her boyfriend, NBA star Devin Booker

While appearing on The Tonight Show Tuesday, the Keeping Up with the Kardashians alum, 25, told host Jimmy Fallon about learning of sister Kylie Jenner's pregnancy news (she's expecting a second baby with rapper Travis Scott), as well as whether she's a good babysitter for her siblings' children.

"I'm alright. I always wanna be the 'cool aunt' and liked, I guess, by all of them," Kendall said.

"I have a lot of them," she said of her of her 18 – going on 20 – nieces and nephews. "But it's fun. It's really fun. I try to be chill — I stress about enough already."

Speaking on whether her NBA-player boyfriend Devin Booker, 24, is close with the younger extended family members, Kendall said, "He loves them. Him and Stormi have an amazing relationship. She has the biggest crush on him, and I'm, like, jealous sometimes. I'm like, 'Stop. Can you guys not?' "

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Kendall has spoken out in the past about being the only one out of her sisters without a baby, but in March 2018, she made it clear she was drawing the line at being an aunt for the time being.

"I have moments when I'm like, 'Do I have baby fever? Do I want a baby right now?' But I don't, I don't," she said on The Ellen DeGeneres Show at the time. "I'm good. I can wait for a little while longer."

"But it's awesome because I have all these little babies to play with, so I can play with them and then just give them back," Jenner joked.

"They're all really cute," she admitted of her nieces and nephews. "It adds a lot of pressure."

When Kylie, 24, confirmed her pregnancy news on Instagram earlier this month, the Kardashian-Jenner sisters congratulated her in the comment section, including Kendall, who declared, "I can't handle it 😫🥰❤️."