Well Heaven, as any child who cries at having a painful operation comes to realise, there is usually a reason.
What if the child were determined to hate his father who sent him for chemo? Even a child could understand that, in the longer term, there was a good reason.
There's a reason for our Heavenly Father's inaction too, but it seems people would rather enjoy their hatred than consider they might be mistaken. I know its painful to revisit the seat of disppointment - but children manage it. They are made upset, they cry, they go into a lonely corner,... but they don't build a barrier, they don't say "never again". They wipe their eyes, they try again - perhaps because they're too young and vulnerable and they don't know how to build a shell for themselves - and there is too much in the world that they feel is out there for them to waste blocking out what they do not yet understand. Its only as we get stronger that we feel we can isolate ourselves - but that strength keeps out many things.