Lauren also added three blue-heart emojis to her Instagram post on Monday.
In the pictures, Lauren was wearing a baby blue sundress with a matching pearl headband, and the 37-year-old country singer was sporting a white T-shirt with khakis. Dutton's outfit also matched what his father had on.
For Chris' part, he posted a video of himself swinging a baseball bat that revealed blue smoke.
"Dutty's gonna have a little brother," Chris captioned the video on Monday.
Chris said back in January that he and Lauren were "not trying" for a second baby and he was actually working on getting his "dad bod" back into shape.
"Every time I'm eating something I shouldn't, Lauren's like, 'Oh, let's make better choices,'" he explained earlier this year. "But having a [toddler], I've definitely not been able to stay in the kind of shape that I have been in for quite some time, but I'm getting back."
Lauren, however, said in March she had "developed a pretty thick skin" in regards to people shaming her post-baby body.
"It doesn't really bother me a whole lot, but it definitely stings more when [comments are made about] my child," Lauren explained. "I've noticed that anyone can say anything about me, and it doesn't really bother me too much."
Chris admitted to Entertainment Tonight the following month that he never really envisioned himself getting married or having kids but meeting Lauren changed his "mindset" on the matter.
"The day [Dutton] was born, and I haven't told anybody this, but I cried my eyes out, because I felt like I was praying, just, 'Lord, thank you so much for not listening to me for all those years that I said I never wanted that,'" Chris said in February.
"I wouldn't have known what I was missing out on and it's truly the best thing in the world."
Lauren competed on The Bachelor's 20th season starring Ben Higgins, which aired in 2016. Lauren accepted a marriage proposal from Ben during the show's finale but they split and called off their engagement over a year later in May 2017.
Lauren previously said how she felt a lot of stress after The Bachelor ended in 2016.
Not only did she choose to move away from her family in Los Angeles, CA, to join Ben in Denver, CO, but she was also dealing with headlines about Ben's love for runner-upJoJo Fletcher and the pair quickly jumped into filming a The Bachelor spinoff, Ben & Lauren: Happily Ever After?, which aired on ABC's Freeform sister network.
Lauren acknowledged to Us Weekly that being engaged when her fiance had just been in love with another woman was "a really hard place" to start off a relationship in the real world. She eventually hit rock bottom during her relationship with Ben.
After a year-long romance with real estate investor Devin Antin ended in Summer 2018, Lauren and Chris sparked dating rumors in November of that year when The Bachelor alum accompanied the country crooner to the 66th Annual BMI Country Music Awards in Nashville.
Not only did Chris and Lauren arrive at the event together, but they also looked like a couple.
Lauren got engaged to Chris in June 2019 and then they got married just four months later in Nashville, TN.
Following their October 2019 wedding, Lauren and Chris welcomed Dutton in June 2021.
Meanwhile, Ben also fell in love with a woman outside of Bachelor Nation, Jessica Clarke.