The newborn infant breathes through his or her nose during the first 6 weeks of life.

http://en.wikipedia.org/wiki/Anatomy_of_the_human_nose

This normal, human embryologic development is exceptionally important — because the newborn infant breathes through his or her nose during the first 6 weeks of life — thus, when a child is afflicted with bilateral choanal atresia, the blockage of the posterior nasal passage, either by abnormal bony tissue or by abnormal soft tissue, emergency remedial action is required to ensure that the child can breathe.