"Happy Birthday to my baby sis @kyliejenner!!!" the new mom wrote via Instagram. "Can't believe your 16! I love you so much!"
Kim, who's been laying low since welcoming her baby girl June 15 alongside beau Kanye West, wasn't the only Kardashian family member to fete Kylie on her special day.
Kendall Jenner, 17, also posted a collage of photos from their fave moments together on her Instagram page and wrote to her little sis, "Happy birthday to my crazy, beautiful, wild little sister @kyliejenner!! I can't believe you're turning 16! I love you and don't know what I would do without you! have an amazing day!"
She added, "Let's party! #woohoo!"
Indeed, the Keeping Up With the Kardashians' teen, currently linked to actor Jaden Smith, will be having a star-studded Sweet 16 birthday party on Aug. 17 at LA's AT&T Center, per The Daily News. The E! cameras will be on hand to film the celebration.
Rounding out the birthday messages was big sister Khloe Kardashian, 29, who tweeted to Kylie, "Happy 16th Birthday to my little peanut @KylieJenner!!!! How are you 16????? The tears…."