An interesting article about the theory of limbo.
Fr. Basil Cole, O.P.
On Limbo: Is Limbo ready to be abolished? Limbo revisited
Nova et Vetera, English Edition,Vol. 6, No. 2 (2008): 403-418
Other related articles -
Fr. Brian W. Harrison, O.S.: Could Limbo be abolished?
International Theological Commission
The Hope of Salvation for Infants Who Die Without Being Baptized