Welcome to Saint West's Jurassic World!

Kim Kardashian and Kanye West's eldest son and second-eldest of their four kids celebrated his fourth birthday with his family on Saturday at a Jurassic Park-themed party.

Kim and sister Khloe Kardashianposted adorable photos and videos from the bash on her Instagram page, including a clip of the guest of honor wearing a carnivorous dinosaur mask handed to him by big sister North West, 6, and momentarily scaring his 1 and 1/2-year-old little sister Chicago West.

"Don't be scared, Chi-Chi, it's just your brother with a mask," Kim tells her.

"It's just Sainty," Saint says.

The kids and their guests, including cousin True Thompson, Khloe's 1/2-year-old daughter, enjoyed jumping around in a dinosaur claw-printed bounce house. Even baby Psalm West got in on the fun!

The outdoor bash was decorated to look like a jungle, complete with a nest of fake dinosaur eggs, lush greenery and a fog machine, which intrigued little True.

There was also a "Jurassic Jewelry" station, and the kids got to pretend to be dinosaurs by wearing colorful claws and tails.

Guests enjoyed a slew of dinosaur-themed desserts, as well as a colorful round birthday cake decorated with M&Ms.

See photos from Saint's birthday party:

Watch Keeping Up With the Kardashians on Sundays at 9/8c only on E!

TAGS/ Saint West , Kim Kardashian , Khloe Kardashian , Chicago West , North West , Birthdays , Celeb Kids , Kardashian News , Top Stories , Apple News , VG , Kanye West , Psalm West