其实这里 用 taken by the children 是过去 分词 短语 作 some photos 定语,而 which were taken by the children 是定语从句作定语,这两种形式都可以作定语.这里 回答是个省略句,补全就是 Some photos （ taken by the children是定语修饰主语） are on show in the museum .但是some photos taken by the children里面没有谓语啊。
taken在这里不是谓语吧？taken by the children过去分词本身就是非谓语动词，在句中作定语.