Baby have 305 bones are there. In growing time it is joint to form 206 bones are later.
Newborn babies have around 300 bones. This is necessary because a naturally delivered baby needs to be, frankly, somewhat compressible in order to fit through the birth canal, which is a comparatively small space. Having more bones means that there are more points at which the baby's body could bend and deform in order to squeeze through the birth canal (for example, babies are typically born with cone-shaped heads because the bones of the skull are not fused, allowing it to bend and become narr
 narrow enough for birth). However, obviously, an adult would not want all these random bending points all over his/her body, since they represent weak points in the skeletal structure. Thus, throughout young adulthood (until the around mid-20s), the separate bones (mostly in the skull/cranium and in the pelvic area) fuse together into single units, resulting in fewer total bones overall. 

Children have more bones than adults because their skeletons are growing. This growth takes place at the 
 This growth takes place at the epiphyseal growth plates. These growth plates are usually at the end of the bones which terminate the bones at a joint. Other growth plates are in areas such as the skull. The skull's growth plates join each other in "suture lines" which are like interlocking fingers. 

Once the skeleton has completed growing, the growth plates calcify and fuse together. This fusion results in few bones in the adult skeleton. Children are born with over 300 bones, many of which f
 fuse together as they grow. The average adult is left with 206 bones.
When an infant borns, it has 300 bones.As it grows big, the bones which are not being used gets joined with each others.As a result a adult has 206 or 207 bones.