Chrissy Teigen & John Legend's daughter is on big sister duty.

The cookbook author showed just how seriously the "All of Me" singer's daughter Luna takes her role as the oldest sibling in a recent social media post. Chrissy, 37, shared a series of snaps the 6-year-old spending time with her siblings, Miles 4, and Esti, 2 months.

In one photo, Luna is holding Esti while another picture showed Luna and Miles under an umbrella in the rain. A third saw the sister-brother duo baking cupcakes with vanilla frosting and green sprinkles.

Chrissy captioned the sweet snaps, "Told Luna to take care of the house while I was gone and she really did."

The sibling bonding time came just a few months after Chrissy and John, 44, announced the newest member of their family on Jan 13. And since then, they have shared adorable moments of their youngest on Instagram, including a video of Chrissy and John kissing Esti on each cheek.

Chrissy captioned the adorable Feb. 28 clip, "First kiss," with a sandwich emoji.

As for how the two older kids are adjusting to having a new baby around? 

"We didn't know how a third kid was going to play with the first two," John shared on Today March 15. "But they are being so good about it. They have been such good older siblings."

And it seems things have turned into a friendly competition between Luna and Miles when it comes to their little sis.

"They're holding her all the time," the Grammy winner continued. "Luna likes to feed her and now they are competing to see who can be the best older sibling."

John added, "She's just brought a lot of love and extra energy into the house."

Esti's arrival comes two years after Chrissy suffered a pregnancy loss with the couple's son, Jack. After announcing her pregnancy in August, the Chrissy's Court star reflected on her journey.

"The last few years have been a blur of emotions to say the least," the heartfelt Instagram post read in part, "but joy has filled our home and hearts again. 1 billion shots later (in the leg lately, as u can see!) we have another on the way."

She noted, "I don't think I'll ever walk out of an appointment with more excitement than nerves but so far, everything is perfect and beautiful and I'm feeling hopeful and amazing."