Kourtney Kardashian commented "Little tiny goose bunny", while Kendall Jenner commented, "what it do babbbyyyyyy."
Kim, who is also mum to North West, Saint West, Chicago West, shared the first-ever photo of Psalm in mid-May, while also announcing his name.
The announcement post was a screenshot of a text conversation between Kim and Kanye, in which the rapper sent his wife a photo of their newborn son sleeping in his crib.
"Beautiful Mother's Day," the text from Kanye read. "With the arrival of our fourth child we are blessed beyond measure. We have everything we need."
WATCH: Kim Kardashian Gives Khloe Kardashian A Very Cheeky Gift For Her Birthday.