现在进行时格式应是Be +动词ing 形式,为什么There are many children playing和I s

现在进行时格式应是Be +动词ing 形式,为什么There are many children playing和I see some men flying kites(选自冀教版英语七年级18课）也可以成立?
大家回答的都不错

进行时用作谓语时,是系动词+doing.
但是这两个句子中,doing不是谓语,而是现在分词短语做后置定语,定语,自然没有动词,否则就成了谓语；额.
现在分词作后置定语是现在分词的一个典型用法
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.现在分词的用法：
1) 做表语：
He was very amusing.
That book was rather boring.
很多动词的现在分词都可以作表语：
exciting,interesting,encouraging,disappointing,confusing,touching,puzzling.
2) 作定语：
上面所出现的现在分词都可以用作定语,修饰一个名词：
That must have been a terrifying experience.
I found him a charming person.
现在分词短语还可以放在名词的后面修饰名词,相当于一个定语从句：
There are a few boys swimming in the river.
There is a car waiting outside.
3) 作状语：
现在分词短语可以表示一个同时发生的次要的或伴随的动作：
Following Tom,we started to climb the mountain.
Opening the drawer,he took out a box.
Taking a key out of his pocket,he opened the door.
现在分词短语还可以表示原因,相当于一个原因状语从句：
Not knowing her address,we couldn’t get in touch with her.
Being unemployed,he hasn’t got much money.
现在分词短语还可以表示时间,相当于一个时间状语从句：
Hearing the news,they all jumped with joy.
Returning home,he began to do his homework.
Jim hurt his arm while playing tennis.
Be careful when crossing the road.
Having found a hotel,we looked for somewhere to have dinner.
Having finished her work,she went home.
4)作宾补：
现在分词在一些动词之后可以做宾语的补语：
例如,see,hear,catch,find,keep ,have 等.
I see him passing my house every day.
I caught him stealing things in that shop.