Child as she is,she can take care of her younger sister.为什么child要倒装在前边呢?是因为只要有as的倒装句,都要把谓语后的都倒装在前面来嘛?怎么is没有在前面呢?

是因为有as，要把child倒装到开头~

这个是一个由as引导的强调句。被强调的部分child，倒装放在前面，表示强调！

as / though引导让步状语从句时,一般须用部分倒装
1. 表语的倒装
一般直接将表语提前到句首,若表语是带不定冠词a / an的单数可数名词,倒装后,不定冠词a / an须被省略.如：
Fine as / though he looks, he is ill with some serious diseases.
Child as / though he is, he knows much about the society.
2. 原形动词的倒装
A. 动词前面带有情态动词may, might, will, would, can, could等时,只将行为动词提到句首,而这些情态动词保留在原处.
B. 若动词前面没有情态动词时,应在动词原来的位置加上助动词do的适当形式.
C. 用于这一句型的动词一般是不及物动词,而不能是系动词或及物动词.如：
Swim as / though he can, he can’t swim so far. 尽管他会游泳,但是他游不得那么远.
Run as / though he did, he didn’t run fast enough to catch the bus. 虽然他跑,但是他跑得不够快而没有赶上汽车.
3. 状语倒装
In the classroom as / though he stays, he doesn’t read his texts. 尽管他呆在教室里,但他不读书.
Carefully as / though he worked, he made some mistakes. 尽管他工作很细心,但还是除了一些差错.

因为Child是主语，他要表达的是像她这么大的孩子，孩子当然是主语放前头，不然怎么放都不能表达那个意思啊