Dear Paul, I think others are probably more able to answer your question, but I will give you my input. Anyone correct me if I am wrong.
I believe when a person is not able to understand the gospel, he/she is not able to repent, therefor would not be able to make a choice to turn from sin and accept the Lord Jesus Christ as savior.
I believe God in those cases considers them like children, and they are accepted in the Kingdom of God.
Mat 19:14
But Jesus said, Suffer little children, and forbid them not, to come unto me: for of such is the kingdom of heaven.
Mat 18:3
And said, Verily I say unto you, Except ye be converted, and become as little children, ye shall not enter into the kingdom of heaven.