Why nursing and not medicine?

Medicine does have specific branches but you decide which one you do once you graduate.
It's important for future doctors to get a good understand of the physiology behind all the different systems in the body and not focus on one- this is because they all intertwine and link and knowing how they effect each other is important. When they specialise later on, the foundation they learnt of the general medicine of the human body will be needed for all specialities (essentially, some parts will be more important than others).

But I mean as a junior doctor the care for children compared with adults is different. Especially their anatomy.

Which is why specialisation occurs then
However as a medical student you learn how the body grows from conception through to adult hood and at what points abnormalities may arise
The anatomy that is different is very limited though as in general you are just growing and getting bigger. How the kidney works in a child is the same as an adult, care of course is different but you still need to learn the same underlying principles

Why is nursing specialised from the start then?

But I mean as a junior doctor the care for children compared with adults is different. Especially their anatomy.

My knowledge on nursing itself is limited but based on my current understandings of the job it is a lot more on the caring side and more practical and following an order given (taken observations, giving medications etc.). How this is done will vary between the different types of nursing and the way it is approached. What you do with a child is different to an adult. As a child nurse you don't need to know how to do something with an adult, wherelse as the doctor there is overlaps in the underlying physiology and so you need to know both sides
Is this sort of making sense? (It's harder for me to talk about the nursing side but this is how I percieve it)

The older an adult, the more likely they are to have multiple things wrong. So a broken hip lady may well have asthma and diabetes. We have to be able to deal with them all.

When I trained.... when dinosaurs roamed the earth.... we did training placements all over the place. So I did general adult medical, general adult surgical, geriatrics ( don't call it that now), accident and emergency, theatres, paediatric, maternity, mental health and district. It was a very good training and made us more rounded than the nurses of today. It made me realise I didn't want to do paediatric nursing.... too traumatic and they bite. Or mental health nursing... too traumatic but they don't bite. Definitely not theatre nursing. Too gory and I ended up holding amputated limbs day after day.

Oh I get it now Thankyou. I'd find adults more traumatising especially if their health gets worse.

Why do nurses have branches like adult, child and mental health but medicine not have any specific branches. I'm going to go on anon because I probably sound stupid.