Maybe this would be better off in AIBU - just feel nine year olds (Year 5) are too young to know about this stuff yet. Surely, secondary school is more appropriate for this? They've done WWII - how evacuees lived but didn't cover the actual fighting on the front line or the politics behind the war.
The Holocaust though - it's heavy duty, serious stuff and I don't want to send him off to bed with nightmares - any tips or good web resources to cover this subject with primary aged children?