John K. Goodrich, “Guardians, not Taskmasters: The Cultural Resonances of Paul’s Metaphor in Galatians 4.1-2.” Journal for the Study of the New Testament. 32:3 (2010): 251-284.
In this article Goodrich seeks to show that Paul is not referring to the Exodus motif in the use of this metaphor. He defends the traditional position that this is to be read against the backdrop of Graeco-Roman guardianship laws. The full abstract, and article if you have access, is available here.