A 12-year-old might need to be shown that raiding the biscuit tin without asking permission is acceptable, but that borrowing a parent s clothes without permission is not.
分析主干：A 12-year-old might need to be shown that... but that...
本句是show sb. that...结构的被动语态，that 从句依然充当宾语。宾语是but 并列连接的两个that 引导的从句。两个从句都用动名词短语(raiding..., borrowing...)作主语。
作者把孩子心急地打开饼干盒的动作称为raiding(袭击)。富有幽默感。
译文：一个12 岁的孩子可能需要人告诉他，不用得到许可就把饼干盒扫光是可以接受的，但是，没有得到许可就借走父母的衣服是不能接受的。