Why does it say "Samu Feneihem Lavo Eretz Egypt Lagur Sham"?
Malbim: There were two groups among them. One came to Egypt to remain there - the army officers and the intentional sinners. Others were taken Bal Korcham (against their will) with the officers - "va'Yikach Yochanan ben Kare'ach Es Kol She'eris Yehudah" (43:5). They wanted to return to Yehudah. Here it says that the first group will be totally eradicated.
Why does it say ba'Cherev ba'Ra'av Yitamu mi'Katan v'Ad Gadol ba'Cherev uva'Ra'av Yamusu"?
Malbim: Primarily, adults die via the sword in war, for they fight. They do not starve, for they seek food. Minors die via hunger and not via the sword, for they do not fight. Now minors and adults will be equated, to die via by the sword and hunger.