Medical retirements normally decided by Drs and they will need access to your records to decide whether you meet the criteria.
When I worked in the Civil Service, our process was to ask OH whether medical retirement was an option. If yes, they would prepare all of the medical file and send it to HR in a sealed envelope marked strictly for the attention of the Scheme Administrator (who was the Dr). This would be sent with the medical retirement application. Obviously, the employee would need to consent to this.
The medical retirement application would also ask the employee to consent in case the Scheme Administrator needed further info.
Getting the consent at application stage does speed up the process as it can take ages and if the employee wants sight of the documents, this takes time.
What you could do is discuss with your GP what information they will provide. Your GP can advise whether your childhood health is relevant to your application for medical retirement. If it's not relevant, they probably wouldn't include it anyway. I doubt the Scheme Administrator would want to travel through lots of irrelevant information.
One employee whose case i oversaw (from a HR perspective) sent me all of their consultant reports and I sent this to the Scheme Administrator and the application was approved really quickly. All of the documents were about current, relevant health matters and I didn't see anything related to childhood.
There is lots of legislation around medical records and it's all very strict and hospitals/gP know what to do with regards to releasing info.