Would one use "my" with darling (ie "ma chérie") to refer to a lover only, or can one also use it to refer to their child, or maybe a friend? How does using "chérie" on its own differ?
Mon chéri and ma chérie can definitely be used with sons and daughters too.
Between friends or colleagues, "ma chérie" is sometimes used, often but not always with a humorous and/or sarcastic way.
Chéri and Chérie alone are almost exclusively limited to lovers.
As a native speaker I can tell you that you can use "my" (as in "Comment vas-tu ma chérie ?) for intimate people lovers, sons and daughters, even best friends (even if it may only be used by women).
BUT, you would only use "chéri" without pronoun for lovers (as in 'Comment vas-tu chérie ?' )