While TBK did explore whether the sacrifice of Jesus can justify salvation for all, the torture of that kid in Omelas would more closely mirror the torture of innocent children in Ivan’s examples in TBK.

Ivan Karamazov quite clearly thought that paradise and the entirety of knowledge are not worth the tears of a single innocent child, and that’s exactly what Le Guin was discussing - not a single willing participant to be sacrificed, but a child who doesn’t even understand why he’s suffering.