Do parents have a right to view their minor child's medical record?

Not in this case, no. The medical report belongs to the employer, not the child.

usually yes, but I do not know, since this is not maintained by the child's doctor This record would be maintained by the employer or the employer's doctor, so you likely may not see it. Do you think, if your child is old enough to work, they are old enough to have some confidentiality. If you really want this, take your child to your doctor, and have your own test run.

Generally yes, if the child is a minor the parents generally have a right to see their medical records.