Questions about the dynastic ruler's children and possible succession scenario arose with the apparent second child's repeated appearances in public in public in recent months.
His young daughter Kim Ju Ae also attended. Some observers interpret this as Kim's message that nuclear weapons will protect future generations of North Koreans.
North Korea is marking a key state anniversary Friday with calls for stronger loyalty to Kim Jong Un, but there was no word on an expected military parade amid heightened international tension.
North Korea's Kim Jong Un vows to develop more powerful means of, days after the country's first intercontinental ballistic missile launch in more than four years
The U.S. is also proposing U.N. sanctions in response to North Korea's six ballistic missile launches since September, each of which it says "were in violation of UN Security Council resolutions."
In a speech at a key political conference, Kim Jong Un vowed to further bolster his military capability, maintain draconian anti-virus measures and push hard to improve the economy.
As North Korea's dictator marks a milestone on Friday, he might be facing his toughest moment yet, as crushing sanctions, the pandemic and growing economic trouble converge
Earlier this week, the U.S. and other leaders of the Group of Seven wealthy nations issued a statement calling for North Korea to abandon its nuclear program and return to talks.