While Hilary Duff's newborn daughter isn't even two months old yet, her 6-year-old son, Luca, is already in contention for the title of Best Big Brother.

The Younger actress sat down with ET's Katie Krause on Thursday, at Love Leo Rescue's 1st Annual Cocktails for a Cause Fundraiser at Rolling Greens in Los Angeles, and the new mom opened up about her baby girl for the first time since giving birth, and marveled at the "amazing" sibling dynamic between her young son and his baby sister, Banks Violet.

"Honestly, it’s like she’s always been there," Duff, 31, said of her little girl, whom she welcomed with boyfriend Matthew Koma, also 31, on Oct. 25. "Obviously a newborn needs their mom the most and when I start to feel bad that she consumes most of my time, I look at him and he’s totally fine."

Luca -- whom Duff shares with ex-husband Mike Comrie -- also has a whole lot of affection for his new sister, Duff shared, adding that he really enjoys spending time with the new bundle of joy.

"He’s so loving towards her and is always, like, holding her face and wants to hold her," Duff said. "When she starts to cry he’s like, 'Mom, she’s gonna blow! Get her!’ It’s really sweet. It's like she’s always been there and he’s just cool."

Duff also had a lot of appreciation for her boyfriend and parenting partner, whom she's been dating since January 2017. 

"Matt’s amazing," the actress gushed. "He’s a really good dad and he’s patient with her."

While she's enjoying the experience of being a new mom once again, Duff admits that it's definitely a lot of work, but she's not one to lament the additional responsibilities.

"Honestly, I feel like I can’t complain about it because people have more than two kids and I’m sitting here like, 'How do people do this? Oh my gosh!'" Duff shared. "By 5 p.m. at night when it’s like school pick up [time] and [Luca] usually has an after-school activity and I’m like nursing the baby at the after-school activity, and then we’re like running home, and [there's] homework and dinner and bath time and trying to be fun and continue our regimen, And I just have a baby on my boob the entire time."

"It’s insane and amazing at the same time and you just do it," she added. "You just figure out a way to do it. But I don’t know if we call it balance yet. It’s mayhem."

While Duff and Koma are busy juggling two kids, the happy family also share four dogs, who add to the chaos, but also have a lot of love for her little ones.

Regarding her involvement at the Love Leo Rescue gala benefit, Duff admitted, "I’m a huge dog lover and always  grew up with dogs." Now, her children are continuing that tradition.

"My little one is 6 weeks old, so she’s like, 'What’s this thing licking my face?'" Duff joked. "But Luca is obviously obsessed with the dogs. He and Momo, in particular, have quite a rowdy 30 minutes before bed, and Lucy won’t eat unless Luca feeds him."

Check out the video below for more on Duff's adorable kids and her growing family.

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