Kim, who is set for his fourth World Cup appearance, acknowledged the emotional cost of being away from his family.
"I am really sorry that I couldn't be with my wife for the birth, and I want to bring home good results from here as my presents," he told reporters on Sunday before a training session at Chivas Verde Valle in Zapopan, near Guadalajara in Mexico.
With more than 80 caps for South Korea, the experienced FC Tokyo goalkeeper faces competition for the starting spot from Jo Hyeon-woo.
The tournament also carries a sense of finality for Kim, who suggested this campaign may mark the end of his World Cup journey. Despite that, his enthusiasm has not dimmed.
"I've played at every World Cup thinking it could be my last. Given my age now, this one really does feel like my final one," he said.
FIFA World Cup 2026
The 2026 World Cup will be held from June 11th to July 19th in the United States, Canada and Mexico. The tournament will feature 48 national teams and will be played in 16 modern stadiums.
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"I am just as excited about my fourth World Cup as I was about my first one.
"The first match will set the tone for the rest of the tournament, and so there will be some pressure. I will try to stay calm and just do what I can do."
South Korea have been drawn in Group A with co-hosts Mexico, the Czech Republic and South Africa. They begin their campaign against the Czechs in Guadalajara on June 11.