إني كنت أعلم منك أنك لو كبرت لعصيت فدخلت النار
I knew that, had you grown up, you would have disobeyed and entered the Fire.
The reply invokes divine knowledge of a counterfactual: what the child would have done had he reached maturity. Knowledge of an unrealized scenario is distinct from the moral evaluation of an act that actually occurred.
Within the dialogue this answer portrays early death as sparing the youngest brother from punishment in the supposed later course. Yet if the general rule is that God must always secure what is best for each person, the second brother can now raise a parallel objection.