1)
Why does it say "Hineni Poked"?
1.
Malbim: This is Hashem's quarrel.
2)
Why will specifically the Bachurim die via the sword?
1.
Radak, Malbim: They trust in their Gevurah, and will go out to fight.
3)
Why will only the children die from hunger?
1.
Radak, Malbim: They will stay in the city. Radak - the fathers will find food and eat it, for their lives have precedence over their children's. Further, they will eat their children's flesh due to hunger!