Your question is a good one. There are likely many pros and cons around the use of a spinal brace for a child like this with a spinal cord injury. The brace does restrict breathing, activity, and motion. It certainly reduces independence.
The brace may be a temporary treatment when the spine is healing and movement must be eliminated. If the spinal bones are broken and/or dislocated, once they are put back in alignment, the brace will keep them there until healing has occurred. Movement could disrupt the healing bones and even cause further damage to the spinal cord and worse paralysis.
In cases of pediatric spinal cord injuries, the advantages of bracing outweigh the disadvantages. Temporary restriction of movement and activity that might result in a stable spine is worth the wait. There are times when the brace prevents (or delays) the need for spinal surgery. That is a very important advantage of bracing.
After the spine has been stabilized, bracing might be needed for spinal deformities such as scoliosis (curvature of the spine) that might start to develop. Bracing is used at the first sign that the spine is starting to lose its anatomic alignment and curve or collapse.
Again, the advantages gained from this type of treatment often make it worth the inconvenience, discomfort, and decreased function for the child in the long run.