Kourtney Kardashian Expecting Third Child

The new addition to the family is due in December and will join siblings Penelope and Mason.

Denise Truscello/WireImage

Three’s company!

Scott Disick and Kourtney Kardashian are expecting their third child, PEOPLE confirms.

“She’s really excited but she’s nervous too,” a source tells PEOPLE. “Three kids is a lot to handle! But she’s happy — she’s always wanted a big family with Scott.”

The new addition to the family is due in December and will join siblings Penelope Scotland, 23 months, and Mason Dash, 4½.

Kardashian, 35, stepped out Tuesday in the Hamptons with sister Khloé after a double dinner date earlier in the week. They’re reportedly in the city to film the latest installment of their reality show over the summer.

While Disick, 31, and Kardashian — who have been dating for eight years — have been open about plans to expand their family, their attachment parenting style had some wondering when it would happen.

“It’s just what came naturally to me. My family definitely all think I’m insane for having [the kids] in the bed and breastfeeding them for forever,” she told PEOPLE while promoting the sisters’ Kardashian Kids clothing line. “I couldn’t care less.”

Mason and Penelope always come first, Kardashian explains.

“Knowing my priorities. Nothing comes before my children. I find that putting everything else in order of importance also helps to get everything done,” she said recently. “Having an amazing partner doesn’t hurt either.”

— Sarah Michaud with reporting by Aili Nahas