Eight-year-old Brooke Davis had long dreamed of being a big sister, so she was happier than ever when she learned at the age of 3 that her mother, Kelsey, was pregnant. But that joy turned to grief when Kelsey suffered a miscarriage, leaving Brooke devastated.

“It was heartbreaking. It really hit me hard … and Brooke especially,” Kelsey, 29, tells PEOPLE. “She was so young and we had been telling her she was going to be a big sister. So she took it really hard. She was completely heartbroken.”

Kelsey says that Brooke was so crushed over the loss that neither she nor her husband Stefan, 29, told her about their next two pregnancies, which both ended in miscarriages. The family, however, welcomed a little girl, Ellie, in 2016 — Brooke was so excited, she asked to be in the delivery room.

About a year later, Kelsey learned she was pregnant again, and was eager to tell Brooke the news.

“She cried really hard. She broke down with excitement,” Kelsey says of the moments she told Brooke they were expecting. “I asked, ‘Are you scared? Are you nervous?’ She said, ‘No!’ She was just so overwhelmed with emotion.”

Brooke took her doting sister duties to a new level, asking her mother if she could help deliver her new little sister, Summer.

“It was all her idea. For Summer, she wanted to be a little bit more involved. Brooke just got so excited,” Kelsey tells PEOPLE. “She was my little helper along the way. She massaged my feet. She walked with me around the halls … she got me water. She was so sweet the entire time. She was right there with me.”

Photos of the delivery showed Brooke in tears as she lifted Summer, who still had her umbilical cord attached. Other shots showed the 8-year-old crying into her father’s arms, and placing a hand over her heart.

“It was perfect. It was the most calm, serene birth I could have ever imagined it being,” the mom of three says. “It was exactly what we wanted. Seeing Brooke there, seeing Brooke’s emotion and helping her deliver Summer, it completely just melted my heart.”

Of the experience, she adds: “Brooke is not traumatized. She’s so glad to have been there and she learned so much.”

Now, the stay-at-home mom says life is hectic with “wild child” Ellie, “sweet” Brooke and baby Summer. But Kelsey adds that Brooke is the perfect little helper.

“She is such an amazing big sister. It just blows me away how great she is,” Kelsey tells PEOPLE. “She’s just so helpful with holding the babies, getting clothes for them. She’s so sweet. She plays with them and talks with them. Ellie’s first word was ‘Brooke!’ “