Why children`s have 33 vertebrae either adultshave 26 vertebrae

As you know in human skeleton two types of bones are found i.e., Axial(80) and Appendicular(126) and vertebral column comes under Axial. Vertebral column of children consist of :Cervical-7Thoracic-12Lumbar-5Sacral-5Caudal-4And in an adult the 5-Sacral and 4-Caudal get fused and forms two different bones and making total bones no. =26