This value you can store along with the child object, to know where to draw it in relation to the parent.
Solving 2) is more complicated.
You want to be able to rotate the child object's position around the parent.
To do this you need to:
Find the current rotation of and distance to the child object
change the rotation by the wanted amount
calculate the new position using cos and sin (you may want to read up on these)
basically cos(angle) gives you the X coordinate of where to position something, and sin(angle) gives you the Y coordinate.
Getting the rotation of a Vector2 is possible using the Atan2 function: