I don't know about the 'brain' but his Mum and Dad should both teach him the same way. It's true enough that when we see wild Children, we should 'pretty much' blame it on the parents or carers. Often when Mum has one set of rules, and Dad has another, it makes for seemingly thoughtless Children, they are mixed-up. '9' is a good age to fix this, set rules, have talks, teach compassion for animals, let them take care of their teddies etc. It's all learning about life and social interaction.