Kathy Hilton Loves Hosting Her Grandkids for Slumber Parties: 'We Make Feather Beds on the Floor' (Exclusive)

She's a former star from Real Housewife of Beverly Hills, an entrepreneur and a philanthropist who spends much of her time traveling the world. But Kathy Hilton says she's happiest as a grandmother — and she cherishes any time she gets to spend with her growing family.

"I feel so fulfilled," she tells PEOPLE, of having so many grandkids. "Eight grandchildren. Can you imagine? I say right now is the happiest time of my life."

Hilton says she recently spent the past Mother's Day with daughter Paris and her kids Phoenix, 16 months, and London, 6 months. Son Barron also joined in the festivities with his wife Tessa and their three kids Milou Alizée, 4, and son Caspian Barron, 20 months, and son Apollo Winter, 2 months.

"It was so special," Hilton, 65, says of the magical day.

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"Nothing makes me happier than to have all of my children and the grandchildren under one roof," she adds.

She says she especially loves watching Nicky Hilton-Rothschild's daughters, Lily-Grace, 6, and Teddy, 5, when they're visiting in Los Angeles and come to her place for slumber parties. (Nicky is also mom to son Chasen, 2).

"They come here and we do a sleepover and we put down a little bed — we make them a little feather bed with blankies and all of that. And they have a sleepover with us on the floor, Papa and I. And that way Nicky and James can sleep in a little in the morning."

Hilton jokes, "We're going to need more space, I tell you! Especially for family trips."

Earlier in the year, it was announced that Kathy and "Papa" Rick Hilton had put their Hamptons estate up for sale. Kathy says she had nothing but fond memories of spending summers there when Paris, Barron and Nicky were young.

Hilton tells PEOPLE, "We used to spend all our summers there," she says, adding they'd go out in winter too.

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"When we lived in New York with all the children, believe me, we were so excited to get out of the city. I love the city, but to just have a place where the kids could run around? It could be icy in the driveway from snow the night before, and we would barrel right in our SUV and put the fire on and just enjoy it so much."

In a statement to The Wall Street Journal  at the time, Rick said, "The layout is perfect for comfortable living and entertaining. We have countless happy memories there."