Koma, 32, debuted the new ink on Instagram Tuesday, sharing a black-and-white photo of the tattoo, which is Luca, 7, and 1-year-old Bank’s hands sweetly clasped together.
“Luca (7) and Banks (1) holding hands just after her 1st birthday. Thank you @curtmontgomerytattoos for engraving my kids,” Koma captioned the post, tagging both tattoo artist Curt Montgomery and Duff, 32.
Duff and Koma welcomed little Banks — their first child together — in October of last year.
“Banks Violet Bair this little bit has fully stolen our hearts! She joined our world at home on Thursday afternoon and is absolute magic,” Duff wrote along with a portrait of herself cradling their baby girl with Koma at the time.
Duff shares son Luca with ex-husband Mike Comrie.
In May, Koma popped the question to Duff, to which she happily said yes. The Younger star shared the moment on Instagram, showing off her ring in two sweet selfies of the couple.
“He asked me to be his wife,” she wrote in the caption.
Koma posted the same photos, writing: “I asked my best friend to marry me… @hilaryduff.”
Since expanding their blended family, Duff has shared a number of adorable and hilarious moments with her kids, including a time where Luca scolded his famous mom about doing a better job of keeping an extra close eye on baby Banks.
In an interview with PEOPLE on Sunday at the Happy Little Camper + Veeda launch party, Duff explained that Luca “doesn’t want her to ever fall off the couch… sometimes I’m like, ‘I swear I’m a good mom.'”
“He’s like, ‘Well, you need to watch her,’ ” she continued in her conversation with PEOPLE. “I’m like, ‘She’s gonna fall down. She’s got to learn not to go near that’ or whatever. I sat him down once and said, ‘Hey, you survived and I was your mom, so I swear she’s going to be okay.’ “
Despite Luca’s eagle eye, “He will not change the diaper,” Duff said of her older child. “But he’s very helpful and he’s just on top of her.”