The dorsal vertebrae range from the bottom of the neck to the top of the pelvis. Dorsal vertebrae attached to the ribs are called thoracic vertebrae, while those without ribs are called lumbar vertebrae. The sacral vertebrae are those in the pelvic region, and range from one in amphibians, to two in most birds and modern reptiles, or up to three to five in mammals. When multiple sacral vertebrae are fused into a single structure, it is called the sacrum. The synsacrum is a similar fused structure found in birds that is composed of the sacral, lumbar, and some of the thoracic and caudal vertebra, as well as the pelvic girdle. Caudal vertebrae compose the tail, and the final few can be fused into the pygostyle in birds, or into the coccygeal or tail bone in chimpanzees (and humans). Fish and amphibians
The vertebrae of lobe-finned fishes consist of three discrete bony elements. The vertebral arch surrounds the spinal cord, and is of broadly similar form to that found in most other vertebrates. Just beneath the arch lies a small plate-like pleurocentrum, which protects the upper surface of the notochord, and below that, a larger arch-shaped intercentrum to protect the lower border. Both of these structures are embedded within a single cylindrical mass of cartilage.
During this age if a child is not moving his legs on his own then it is recommended to do some exercise, especially gentle stretching with the child. 1 to 3 years
“This is the age at which the characteristics of diplegia become more noticeable, mainly because, unlike other children at this age, the child with diplegia is not walking.”  By the age of three, it is important for the child to be in a specialized school environment so the child can participate in physical therapy and learn social skills. Parents should not force the child to sit, crawl, or walk a certain way during this age period. Let the child do whats comfortable for them and allow the therapist to correct this problem. If you want to help your child walk more, then push toys are recommended for walking aids. Regular exams should be done to make sure the childs legs are growing normally and he or she is not having any problems with the hip. 4 to 6 years
“This is the age range at which the child with diplegia makes the most significant physical improvement in motor function.”  During this time period the child makes major improvements in motor function. He or she should be in a regular school and focus on cognitive issues not therapy. A child using a walking aid for mobility to move around with the other children is not a bad thing.