Answer: During the development of fetus, tissues of face and mouth didn't fuse properly so they remained open when the fetus was in the process of development.
Explanation: Many factors can cause this condition such as exposure of a mother to some environmental conditions, what mother eats during pregnancy like some medicines, alcohol. May be the parents contained the gene that can cause this condition. This condition is inherited sometime if there is the history of this condition in the family. Sometimes, obese and diabetic women also gives birth to a baby with the condition of cleft lip and cleft palate.