Throughout the day, the group was spotted riding It's a Small World, the Merry-Go-Round and other attractions near Fantasy Land.
And with Christmas right around the corner, Kourtney couldn't help but get in the holiday spirit by wearing festive-themed Mickey ears.
Before heading to Disneyland, the proud mother-of-three shared a heartfelt message to her boys on her popular app.
"How crazy is it that I have two boys born on the same exact day?" she wrote online. "It is truly so special and meant to be. They changed my heart forever. Happy birthday to the coolest brothers I know!!!"
And while Khloe Kardashian was unable to make the trip, she certainly didn't forget to wish the birthday boys a special day.
"Born to be besties!!! Happy birthday to the special boys who share the same birthday!" she shared on her website. "God blessed you with a sibling soul mate and I'm so thrilled to be your auntie. Watching you grow up has been one of the greatest joys of my life!"
Kris added, "Happy birthday to these two sweet boys!! Our precious angels Mason and Reign. I love you more than words can say."