I’m not aware that 14yr old boys becoming aroused by their 4yr old sisters is a ‘normal thing’.
This wasn’t ‘inappropriate behavior with a teen girl not related to him’. He fondled the four year old while she was in his lap being read to.
There is nothing 'normal' about it. It's pure evil, and of Satan, not of God or having anything to do with Christianity. The only thing 'normal' about it is that each of us is brought into this world in the very same state of soul.