"Salvation Outside the Church? Tracing the History of the Catholic Response" by Francis A. Sullivan S.J. First Published 1992 

Ch. 4 - Medieval Councils, Popes and Theologians

For the most recent teaching of the Catholic Church on Limbo see "The Hope of Salvation for Infants Who Die Without Being Baptized" by the International Theological Commission from 2007:

https://www.vatican.va/roman_curia/congregations/cfaith/cti_documents/rc_con_cfaith_doc_20070419_un-baptised-infants_en.html

ISBN: 1-59244-008-8