Kailyn took it to Instagram to share a photo collage of a few precious moments between herself and Isaac, which she lovingly captioned with a heartfelt message.
"Love at first sight gained a whole new meaning when a I looked at my child for the first time," Kailyn wrote. "'It's a boy!' were the first words I heard after 14 hours of labor on January 18, 2010 and my life was forever changed. The past 4 years have been filled with dirty diapers, first words, laughing, crying, some struggles and everything in between. I cannot express the love I have for this little human being. Wishing nothing but lifelong happiness for my baby, Happy 4th birthday Isaac Elliott! Bring on the waterworks."
Yep, we're crying. Teen Mom 2 fans have been with Kailyn through almost every step of her emotional journey with Isaac, and it's amazing to see how much he's grown and changed in the past four years. Isaac's inspired everyone around him, including his stepdad Javi Marroquin, who also hit up Instagram with a shout-out of his own.
"You first taught me what it was to be a father," Javi wrote. "You opened my eyes to a world I wasn't used to. I hope that one day you'll be proud and hope that we remain best friends no matter how old you get. Happy 4th birthday lil Papi."
Aaand, we're crying even harder. Isaac is so lucky to have such supportive parents in his life! Happy Birthday, lil' man!