Typically new born babies are around 3 Kg in weight (and many of them are much smaller than that, but are healthy enough with a lower weight). Even with a weight of 3 Kg, it takes time and effort for the mother to produce the baby from her body. However, there have been cases in the past when babies with much larger weight have been born, such as happened in Indonesia recently where a baby was born that was atleast 3 times bigger than the normal weight of a new born baby (link to an article, and you can also see a photo):
Muhammad Akbar Risuddin, born Monday, is thought to be the heaviest baby born to date in Indonesia. "I was very surprised. I thought it was twins," said Binsar Sitanggang, the lead doctor in the cesarean-section delivery at Abdul Manan Hospital in North Sumatra.
"We can compare this giant baby with a 9- to 10-month-old baby," Sitanggang said. "Both his parents are tall and big, so there might be a genetic cause for this." Sitanggang said the baby has already developed a robust appetite, requiring instant milk as well as breast milk.
If you see the photo in the linked article, you can see how big the baby actually is.