Children as he is ,he can answer these difficult questions.

Come on.语法错误啊！
Children是复数，he是第三人称单数。
要改成A child as he is, he can answer these difficult questions.[=He is a child, but he can answer these difficult questions.]
尽管他只是个小孩，他可以回答这些难题。
这个句型只能用于转折连接。
如果说An adult as he is, he can answer these difficult questions.那就用错了。
正确用法：Plain as she looks, she is quite caring and gentle. [=Although she looks plain, she is quite caring and gentle.]

as 引导的让步状语从句（表尽管、虽然），如果从句是个表语从句，要用倒装，把表语提前（如果表语是可数名词，提前时前面用零冠词。）

当他还是个孩子时，他能回答一些困难的问题。

as 引导的让步状语从句(“虽然”)要用倒装语序，前面放形容词、副词或名词。如 Large as Australia is, much of the land is sand. / Hard as he works, the leader isn’t pleased with him. / Boy as Mike is, he can look after the baby.（注：名词前不加冠词）
希望我的回答能够帮到你，望采纳！
祝你学习进步，天天快乐。O(∩_∩)O

虽然他还是个孩子,但他能回答一些难的问题