同学你好，该知识点来自沪江网校《英语零基础直达CET4级考试版》的课程，想要更系统的学习，欢迎进入课程学习。不仅可以和更多的同学一起学习，而且还有老师、助教随时的学习指导和知识点解答哦。

同学好，
How many children are there playing on the playground?首先理解这个问句的陈述语序为
There are （how many）children  playing on the playground.
there are是一个固定的搭配，相当于have有的意思。所以是不能拆开的哦。
所以不可以写How many children are playing there on the playground？可以改写为
How many children playing on the playground？

同学可以从这里了解更多there be存在句的知识点哦。
https://www.hjenglish.com/new/p144165/

希望对你有帮助。