Nicky Hilton and Sister Paris Hilton Pose with Sons in Sweet Candid Photo for National Sons Day

Nicky Hilton Rothschild and sister Paris Hilton love having their little boys grow up together.

On Thursday, the mom of three, 39, posted an Instagram photo of her and her son at the beach next to Paris and her 7-month-old son Phoenix. In the photo, the two sisters are sitting in the water while holding up their sons.

"Happy National Sons Day to our sons! 💙 Love doing this boy mom life with my bestie. 😊," Nicky captioned the picture.

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Hilton Rothschild first shared that she had welcomed her son with husband James Rothschild on Instagram in July 2022. Since then couple still hasn't disclosed the baby's moniker.

"We are officially a party of 5!" she wrote on Instagram, sharing a black-and-white silhouette image of the proud parents. "Welcome to the world sweet boy. Mom, dad and big sisters could not be more smitten. 💙."

Along with her son, Hilton Rothschild shares daughters Lily-Grace Victoria, 6, and Theodora "Teddy" Marilyn, 5, with her husband.

In March, Hilton Rothschild spoke with PEOPLE about balancing her life as a fashion designer and a mother. She said during the interview that she's savoring the years that she can select the outfits for her children. She wants to dress them like kids because they grow up fast enough, noting that she's not a fan of children being dressed like adults before their time.

"Balancing my kids with my fashion design business is a never-ending battle," the busy and devoted mom said. "But it's important to set the right example for the children from the beginning."

"My daughters like the colors pink and purple now, and they are girly girls in the sense that they love fashion and dressing up," Hilton Rothschild said.

"My youngest daughter used to tell me that her favorite color was gray. Thankfully that has changed!"