Hi,
This seems a little tricky as you would usually follow the school's policy and procedures and they would state the roles of each professional. Perhaps if you search online for an example of a schools safeguarding policy and procedure this could help and just mention in your work that its a copy as you do not work in a school. Also reference where it is from.
I think you are on the right track with the lines of responsibility, although emphasise the importance of the designated person, as not all the members of staff will be involved in any cases regarding a child's welfare but only those on a need to know basis.
Also, it is the role of all those working with children, from midday supervisors to the class teachers in being aware of the signs and symptoms and when/why/how to deal with these situations.
I know it's a diagram that has been asked for but you could add these points as outlines/bullet points.
Hope this helps