You would generally need the same ones to apply to medicine – choosing child and adolescent mental health (CAMHS) specifically comes later down the line once you have qualified.
It looks a bit like this:
Medical school (5-6 years)
Foundation training where you rotate lots of jobs and work as a doctor (2 years)
Specialty training where you choose psychiatry specifically but work in lots of environments, like on a ward, in CAMHS, in the community etc (3 years)
Higher Specialty training where you would choose to do more child and adolescent rotations if you wanted (3 years)
When I applied for medical school they were more interested in A levels than GCSEs. I think the sciences tend to be the focus, which is a bit of a shame as I think people who do the arts can become great doctors too. The sciences I did for GCSEs were biology, chemistry and physics.. Fro A levels I did Biology, chemistry and maths. Doing child and adolescent psych or CAMHS as it is called is really rewarding and more people are needed in this field