The section immediately below the one you copied explains that you have to have the child’s permission GeandmaC7.
Children's rights, capacity and consent
‘Children have the same legal rights over their data as adults. The GP surgery must get the child's consent before giving access to their online GP services, if the child is able to understand and make an informed decision. This is called having capacity.
Children aged 11 or over are usually considered to have the capacity to consent, or refuse access, unless for example they have a medical condition or learning disability that affects their understanding.’