PHP FPM and PHP CGI

Hi,

I have installed a virtualmin server with multiple version of php on Ubuntu 16.04. (from this https://www.virtualmin.com/documentation/web/multiplephp)
All is good acutally but :
On my site i select FCGI on PHP 7.2.
All work fine but in process list i have apache2 and this have 4 sub process php-cgi7.2
like that :

/usr/bin/apache2
| - /usr/bin/php-cgi7.2
| - /usr/bin/php-cgi7.2
| - /usr/bin/php-cgi7.2
| - /usr/bin/php-cgi7.2

I don’t understand why php-cgi7.2 process run after page loaded.

Can you explain ? It’s normal ? with few days how many process stay ? Every process have memory consuption so …

Sorry for my english, i’m french