each作为形容词,修饰单数名词,接单数动词。作为代词,单独使用,接单数动词;放在复数名词和代词后作同位语,接复数动词。each of them后可接单数或复数动词。如:
Each man carries his own bag. (修饰单数名词)各人背自己的包。
We each have our own office. (作We的同位语)我们各有各的办公室。
Each carries his own bag. (代词)各人背自己的包。
Each of them are/is here. (代词)他们每个人都在这儿。
本题中the children是复数,所以用have