Kim Kardashian split from Reggie Bush in March, but she has another man in her life.
"Good morning kisses w the luv of my life Mason!" the makeup-free reality star, 29, Twittered of Kourtney's 4-month-old son Saturday.
PHOTOS: Stars without makeup
Little sis Kendall, 14, told UsMagazine.com at the Wango Tango show in L.A. Saturday that Kim is enjoying the single life.
Added brother Rob, 23, "She's working. She doesn't even think about it." Said sib Kylie, 11, "[Kim and Reggie] talk...they're friends," but "she's so busy." (Indeed, Kim has been Twittering over the weekend about getting two hours of sleep because she's flying so much -- and avoiding eating Cinnabon in the airport to keep her "own two big backside buns" in shape.)
Kendall said baby Mason is "amazing. He's so good." Mason just began "rolling," added Kendall.
"And he looks like an old man," joked Robert. "And they dress him up real well too."
Kourtney won't be having another kid any time soon, though.
PHOTOS: Adorable snaps of Mason
"You've got to take it slow. Learn from the first one, then get married, then have a baby," said Rob. The Kardashian sibs say they don't know if Kourtney will wed Scott Disick, but agree "he's a great dad," according to Rob and Kylie.
The next Kardashian baby: Khloe and husband Lamar Odom, which will "100 percent happen," Rob said. "It'll be a really tall baby."