The Kate Plus 8 star accompanied the post with a collage featuring then-and-now photos of the sextuplets.
"At this moment (7:51-7:53 am) 13 years ago, my life and heart were completed with your births!," she recalled. "I love you all and NO MATTER WHAT it requires of me, I will ALWAYS be there for you."
"I'll always be your biggest cheerleader, your role model by example, your shoulder to cry on, the hug and laugh you need, and your mommy and friend!," continued Kate. "I love you guys! I got six times what I planned on, but I'd NEVER EVER go back! You're the six final pieces of my heart that I never knew I was looking for."
While fans have watched the sextuplets and their 16-year-old twin sisters, Mady and Cara, grow up in front of the camera, being on TV isn't always easy.
In December, Kate, whose tumultuous relationship with Jon has played out in the press, admitted to making parenting mistakes.
"I mess up, yet it's out of love for my kids that I say, 'I messed up. I need to get better at that,'" she confessed during an episode of the Dr. Oz Show. "I mean, my life is my kids and there just wouldn't be Kate Gosselin if it wasn't for my kids. Everything I do [is] for them. I mean, being on TV is not easy. Having tabloids written about you constantly is not easy."