South Korea’s top spy agency said it is closely analyzing the possibility that children seen alongside Kim Yo-jong, the powerful sister of North Korean leader Kim Jong-un, in video footage from a New Year’s celebration are in fact her own children.

The National Intelligence Service(NIS) made the comment Friday in response to a question from Seoul’s Yonhap News Agency.

In the video from Wednesday played by the North’s state-run Korean Central TV, Kim Yo-jong, deputy director of the ruling Workers’ Party, is seen walking with a boy and a girl outside Rungrado First of May Stadium, where the event took place.

An official at Seoul’s unification ministry said Thursday that it is unusual for the North Korean leader’s sister to be publicly seen holding hands with a child or to attend an event accompanied by family members.

While rumors of Kim Yo-jong’s marriage, pregnancies and family status have never been officially confirmed, the NIS believed in April 2015 that she was due to give birth the following month and that her husband was an alumnus of Kim Il Sung University.

A South Korean government source confirmed that Kim was pregnant, likely for the second time, when she visited the South in February 2018 to attend the opening of the 2018 PyeongChang Olympic Games.