Minor being the key word here. Brains don’t stop physically changing until your late teens/early twenties - simply put when the offender is this young there is a very good chance that it’s not a broken person - but instead is something else causing the behavior (frankly - usually because the offender is being abused in a similar manner).
Outside of actual murder (and even then I have big reservations) - it is wrong to treat children similar to adult offenders. Most of the word actually gets this correct. The United States are the ones out of step.
But kudos for linking a 12 year old to a serial killer cannibal - I mean we totally treat adult rapists like serial killers it is a fair comparison.