"In some cases the kunya is figurative, not referring to an actual child"To elaborate on this, when it's figurative, it means things like "One of, one with, one known for etc". For example, the name of Prophet Muhammad's - peace upon him - companion Abu Huraira - God be pleased of him - translates to something like "One with the kitten". The reason is that he was known for a pet kitten he had.