a) These bodies are not "us" they are only loaned to us by Allah (SWT) ...
b) That to think of a car and inside it is a driver - in a similar way we are inside this body "driving" it to do what we want.
c) Give clues about the ruh
(i) The ruh is invisible we cannot see it
(ii) when a person dies the ruh leaves the body and goes to a different place - for a young child saying that it has gone to Allah (SWT) is enough detail.
(iii) if they ask how did it go ... say that an angel takes it and leaves the body behind.
(iv) explain that each time we sleep our souls are temporarily taken away and replaced when we wake up.
(v) explain that death has a special taste (avoid mentioning the intensity of the pain of death to a young child) that will be experienced by every living creature.
To explain Isa (AS) say that he is a man and God is not a man and God does not have children at all. Say he is a prophet of God just like other prophets. I would teach from a book of 'aqeedah about Tawheed.