Sisterly advice? Loves it!

Nicky Hilton recently shared the words of wisdom she gave Paris Hilton about the first year of motherhood following the birth of baby Phoenix Barron Hilton Reum.

"My advice always is to not miss the small moments," the 365 Style author exclusively told E! News May 18 at an event in New York for the Smirnoff ICE Relaunch Tour. "There's such a short window that they're so small, and new things are happening every day. Like, Paris always says her son looks different every day."

Phoenix, 4 months, is Paris and husband Carter Reum's first child together, with the couple privately welcoming the little one via surrogate in January. 

"She is so happy. She's so content," Nicky shared. "I was just over there last week and just hanging out in the nursery with her and her son, and she's so complete is the word I'd use."

The fashion designer has three children of her own with husband James Rothschild: Lily-Grace Victoria Rothschild, 6; Teddy Marilyn Rothschild, 5, and a 10-month-old baby boy whose name has yet to be revealed.

And as Nicky noted, you can certainly see the family resemblance in the children. When it comes to Phoenix, she said, "He looks a lot like me as a baby, and my daughter Lily-Grace looks identical to Paris as a child. So, it's interesting how the genes crossed like that."

The sisters aren't the only ones in the family to recently welcome a bundle of joy. Last September, their brother Barron Hilton II and his wife Tessa announced the birth of their son Caspian Barron Hilton, now 8 months. (They also share daughter Milou Alizée Hilton, 3.)

"Funny, we had all girls in the family and, in the last year, my brother had a son, Paris had a son and I had a son," Nicky told E!. "So, we've been flooded with boys, and it's amazing to see the bond between them."

So, what does a typical playdate look like?

"It's a lot of parallel playing," she explained, "and we put them on the floor, and they hang out next to each other and we hang out. But that's sort of how it was growing up with my mom, and her sisters, and our cousins and we're all best friends like sisters. We celebrated [Kim Richards' daughter] Whitney [Davis]'s bachelorette in Malibu, which was quite nostalgic and fun, the whole gang being back together."

And the heiress tries to follow the same advice she gave Paris about taking in the little moments. Speaking about her son's milestones, Nicky noted, "He's teething. He's trying to stand. He's trying to talk. He's trying to walk. He's almost saying, 'Mama,' but not quite there yet."

- Reporting by Nikaline McCarley