Sorry, maybe it wasn't clear. You can and probably should increase the max children if you are seeing that message in the logs. You probably have some idea how much RAM your system uses on average, subtract that from the total and as per the linked blog above ps -ylC php-fpm --sort:rss when you are seeing that message in the logs.
Then take your adjusted total RAM (Total subtract average system use) in MB and divide it by the average RSS value of the output from above command. This yields a number you could enter into max_children. You can and should use a conservative value for your adjusted total RAM, because you don't want to end up making the box swap.
Another, possibly simpler method, is to just incrementally increase the max children until you stop seeing that message in your logs.
Your choice. If I set up a web server, say, I try to think, I will dedicate X RAM to the underlying OS, X RAM for mariadb or whatever datastore, X RAM for PHP, X RAM for varnish caching, X RAM for nginx and so on. So the first method will give you a somewhat better idea of how your box *should* generally run, the second is probably going to be ok for personal use too.