Madeline did not tell Bond about her daughter because both her parents were killers.

Bond and Madeleine Swann's child is Mathilde.

In No Time to Die, Bond and Nomi infiltrate Safin's secret island headquarters. Safin plans to kill millions of people using nanorobot bioweapons called Project Hercules.

Bond ordered the destruction of the island with missiles, but before 007 could escape, Safin shot Bond and injected him with a virus that specifically targeted Bond's lover Ma The DNA of Dr. Delin Swann and their four-year-old daughter Mathilde.

Bond chooses to stay on the island that was destroyed by the missiles rather than risk infecting Madeleine and Mathilde and escaping, which would lead to their deaths.