I wasn't quite sure what to make of this section, it is not a theology that I'm familiar with. The author doesn't go into the name of the belief or where it came from, he merely presents it.

The belief that is discussed in this chapter is the concept of "salvation after death".

The teaching is convoluted and depends solely on 2 Peter, where it says that the gospel was preached to those who are dead. That can mean either spiritually dead, or those who were alive when they heard the gospel, but who had died by the time of the writing of the letter.

Applied to infants, this teaching says that when a baby dies, they are brought to a point of maturity where they can hear the gospel and choose to accept it or not.

The problem with this theology is that it is not found in Scripture. It also is akin to throwing your theological hands into the air and stating that the question of where babies go when they die has no answer in this life.

Another problem is that there is no comfort for hurting parents.  Is there child in heaven or not?  There is no answer here, because with this theology the answer does not depend on God's goodness, it depends on the (post-death) choice of the child.

When the Bible speaks of judgement day, and the final judgement, a person is judged on acts committed during their life - not on a choice made after death.

Teaching that a baby goes to heaven or hell, based on their own choice made after they die is not the anser.