naivety       
noun [ U ] (also naiveté) uk/naɪˈiː.və.ti/ us/naɪˈiː.və.t̬i/
 轻信;幼稚
trust based on not having much experience
 disapproving He demonstrated a worrying naivety about political issues. 他在政治问题上表现得很幼稚,真令人担心。 
approving I think her naivety is charming - she's so unspoilt and fresh. 我认为她的天真很可爱——她是这么纯洁无瑕,清新动人。