One photo showed Kailyn baring her stomach in a beige crop top and matching underwear, while she was pictured with a noticeably bigger bump in second mirror selfie. Ultrasound images of her unborn twins were included in her post, as was a sonogram video that transitioned between the two babies in her belly.
The 31-year-old wrote in the caption, "evolution of the twin bump."
The siblings will join Kailyn's son Isaac, 13, with Jo Rivera; Lincoln, 9, with Javi Marroquin and Lux, 6, and Creed, 3, with Chris Lopez. She and Elijah are also parents to baby boy Rio, whose birth was announced in July.
Babies No. 6 and No. 7 are a happy surprise for Kailyn, who previously said she had "no idea" that she would conceive so quickly after welcoming Rio.
"I mean, this is my sixth pregnancy, six and seven for me," she said on the Oct. 27 episode of her Barely Famous podcast. "And I've gotten pregnant when I'm not actually—like, I've tracked my ovulation and I've gotten pregnant on days that were not my ovulation window."
Looking back at her calendar, Kailyn said she "must have got pregnant right before" leaving for her Thailand trip earlier this year.
"When I got there, I was eating everything," the podcaster recalled. "My face was flushed, but I didn't think anything of it because I was like, 'There's no way. There's no way I am.'"
So, is marriage the next step for Kailyn and Elijah then? Not quite.
"I kind of would like to have something to look forward to in the future instead of doing everything all at once," Kailyn told People last month. "I think we have time. If we're meant to be together, then we don't need to rush into it tomorrow."
To see Kailyn's sweetest moments with her kids, keep reading.