"Carmen is decorating her baby brother β€πŸ§‘πŸ’›πŸ’šπŸ’™πŸ’œπŸ’–πŸ˜‚," Hilaria Baldwin captioned a belly-baring photo of herself in a black bra and panties

By Jen Juneau
March 05, 2018 02:15 PM

Alec and Hilaria Baldwin‘s daughter Carmen Gabriela is a budding artist!

The adorable 4½-year-old is completely enthralled in a new snap shared to her mama’s Instagram account, covering Hilaria’s bare baby belly in a variety of colorful heart-shaped stickers.

In the sweet mirror selfie, the mom-to-be is wearing only a black bra and panties (both Heidi Klum Intimates) as her daughter busies herself “decorating her baby brother.”

“Hello 3rd trimester!” Hilaria, 34, captioned the Saturday post.

Want all the latest pregnancy and birth announcements, plus celebrity mom blogs? Click here to get those and more in the PEOPLE Babies newsletter.

Hilaria shares three children total with husband Alec and one more son on the way: Carmen, plus sons Leonardo “Leo” Ángel Charles, 17 months, and Rafael Thomas, 2½.

“Every single time I do this, I can’t believe the elasticity of the human body,” wrote the fitness guru on her Saturday photo. “It’s hard, and I get tired (especially with 3 on the outside), but I feel so lucky to have experienced this in my life.”

“I always tell people that their bodies are capable of so much — and given the right care and fuel, you can really feel good and strong from the inside out ❤. #WeGotThis2018

Watch Hilaria Baldwin talk parenting and more on Mom Talk. Go to PeopleTV.com, or download the PeopleTV app on your favorite streaming device.

Hilaria opened up to PEOPLE in November about her growing family, admitting she “never knew how many kids” she wanted, but “really, really” likes motherhood and is “excited” about her upcoming new addition.

“We were like, ‘Oh, should we have another kid?’ ” she recalled of her conversation with Alec, 59. “We were like, ‘You know what? Let’s try something different — let’s try.’ [With] the other ones, it’s not like we were like, ‘Oh my God, how did this happen?’ But this is the only one we [planned].”