Approximately 300 bones in new born babies later the bones fuses and there are 206 bones in adults.Infant bones are made entirely of soft, flexible tissue called cartilage that's slowly replaced by hard bone as the baby develops.By the age of two,the baby's skull bones become fully fused. Even Chimpanzees and gorillas also have unfused skull bones at birth, but their bones fuse completely together at only three months of age.Over time, most of this cartilage turns into bone, in a process called ossification. As the baby grows, some of its bones fuse together to form bigger bones. By adulthood, your skeleton contains just 206 bones. is the bones of newborn babies fuse at the earliest stage then leads to Craniosynostosis, a condition where one or more of the sutures in a child's skull fuses or closes too early. Sutures are fibrous joints located between the bones in a baby's skull. Open sutures allow the skull to grow at the same rate as the brain. ... This can cause pressure on the growing brain. Therefore for the growth of internal organs like brain etc the outer skeletal framework of newborn babies are free and the bones are not fused or hardened together like adults.