What do you do if the whole class is “not getting it”?

Shoot'em all and go to another class )))

If seriously, explain again and in a different manner

The first thing I should do is to reflect on my strategies and modify accordingly, if this does not work, I should consult my colleagues or supervisors.

 iexplain again and in a different manner

Change the way of explaining things, such as using pictures or demonstrations.

I am sure some students will get the point and be able to explain in their own creative way, as children are highly creative due to their imagination ability in comparison to adults.