Is there a reason for this - birth deformities?

It really has to do with poor living conditions and inadequate health care. A lot of these babies were probably supposed to be twins but because a lack of certain vitamins and minerals, they were not able to fully form in the womb. Luckily though, the cultures in that area feel blessed to have children like that (most) and see them as gods/goddesses and are well taken care of just for that reason. There's a purpose and plan for everything.