I keep a box of old clothes for the children to dress up in

I(主语)+ keep(谓动)+ a box of old clothes(宾语)+ for the children(不定式的逻辑主语)
+ to dress up in(不定式作定语修饰 clothes) .
当然也可把 for the children to dress up in 当作是带逻辑主语的不定式作目的状语.
两种情况,翻译出来的汉语意思都差不多.
句意:我保留了一箱供孩子们乔装打扮穿的旧衣服.(不定式作定语修饰clothes) .
我保留了一箱旧衣服,供孩子们乔装打扮穿.(不定式作目的状语.)