What will happen if humans give birth to a large number of babies at the same time?

First of all that is not possible a person cannot give birth to more than 3 babies at the same time.

A woman gave birth to six babies at the same time and that is the highest record. And very rare.

But to answer your question if there is some magic and whatsoever (according to you) then the babies will not be able to survive.

Our earth will become overpopulated and our Natural Resources will become over.