Below I suggest a number of books; of course, my listing here does not indicate endorsement of all their content.

Historical Works:

Houston, Thomas. The Adoption of Sons, Its Nature, Spirit, Privileges and Effects: A Practical and Experimental Treatise. Paisley, UK: Alex. Gardner, 1872.

Webb, Robert Alexander. The Reformed Doctrine of Adoption. Grand Rapids: Eerdmans, 1947.

Academic Works:

Burke, Trevor J. Adopted into God’s Family: Exploring a Pauline Metaphor. New Studies in Biblical Theology 22. Edited by D. A. Carson. Downers Grove, IL: InterVarsity, 2006.

Scott, James M. Adoption as Sons of God: An Exegetical Investigation into the Background of YIOTHESIA in the Pauline Corpus. Tübingen: J. C. B. Mohr, 1992.

Popular Works:

Johnston, Mark G. Child of a King: What Joining God’s Family Means. Geanies House, Scotland: Christian Focus, 1997.

Ferguson, Sinclair B. Children of the Living God. Colorado Springs: NavPress, 1987.

Ordained Servant Online, March 2016.