The number of bones a person has in their body generally depends on their age. A human newborn baby has approximately 270 bones in his or her body. As the person ages and develops, some of the bones fuse together to make larger bones. By the time a person is an adult, they have the standard 206 bones in their body. This bone development usually ends in a person's mid-twenties. The 206 bones in a human skeleton can be divided into two major divisions. The axial skeleton is comprised of 80 bones and makes up the spinal column, rib cage, and skull. The appendicular skeleton is comprised of 126 bones and makes up the pelvis and extremities (arms and legs).
So the answer to your question is that there is no definitive answer. The number of bones in a seven year old child will range somewhere between 270 and 206. Each specific child's skeleton will fuse and develop at an individual rate; different seven year old's will have different numbers of bones.
The number of bones an individual has varies developmentally. In fact, a person has the most bones when they are born, as an infant has 300 bones. Over the course of development, some of the bones fuse together, so that by the time a person reaches adulthood, the number of bones in the body is 206. Bones in the skull fuse together as do other bones in the body. Thus, the number of bones that a seven year old child would have to be somewhere between 206 and 300 bones.