A child born to a B blood type couple is either B or O. The blood type of the human body is generally determined by the antigens on the surface of the red blood cells in the body, and a B blood type couple indicates that the red blood cells in the parents’ bodies show B antigens on their surfaces. If both parents are B blood type, then the parents’ blood type gene is BB or BO blood type. According to the law of genetics, the child’s red blood cell surface will only show B antigen or no antigen, which is often referred to as B or O blood type. To determine your child’s blood type, you need to go to a regular hospital and have a blood test, which can help you know your child’s blood type quickly and accurately. If the patient has medical needs, please make sure to go to a regular medical institution.