At the time of birth the panda weighs just 4 ounces (100g)
(Image source: youtube)
The weight of baby panda being so less at the time of birth, it becomes tough for the mother panda to care. In few reported incidents at the zoo in China it was found that the mother panda crushed the baby panda while caring for it. Such incidents might happen accidentally.
Amongst the marsupials, Pandas are accounted to give birth to their tiniest younger ones. (A mature mother panda would weigh about 90kgs while the new born baby panda would weigh about 100gms )
(image source: cutest paw)
These new born pandas can neither crawl nor see anything for the first two months after they are born. They rely completely on mother panda for their living.
Mother pandas usually just choose to give birth to only one child and if it case it gives birth to two babies, it would choose to care for only one while abandoning the other one.