First lady Ri Sol-Ju delivered the couple's third child in February, the Yonhap news agency reported Tuesday, citing South Korean lawmakers who were briefed by the National Intelligence Service.
Ri had disappeared for an extended period last year, raising speculation that she could be pregnant.
News of the new arrival emerged as North Korea fired a ballistic missile over northern Japan.
According to previous intelligence reports from Seoul's spy agency, Ri married Kim in 2009 and gave birth to their first child the following year, with their second born in 2013.
Kim is the third generation of his dynasty to rule North Korea, but little has been revealed about the country's first family.
Former NBA star Dennis Rodman, following his trip to the North in 2013, has been the only source of information about the couple's second child -- a baby girl named Ju-Ae.
Saying that he had held Kim's daughter in his arms, Rodman described the North Korean leader as "a good dad" who has "a good family".
While more of a public personality than his introverted father Kim Jong-Il ever was, Kim's own personal details remain little known. Even his exact birthday and the date of his wedding have not been confirmed.
South Korean intelligence reports have described Ri as coming from an ordinary family, with her father an academic and her mother a doctor.
She visited South Korea in 2005 as a cheerleader for her country's squad in the Asian Athletics Championships.
Eyewitness? Submit your stories now via social or:
Email: news@pulselive.co.ke
