I totally believe in the age of accountability. but it is not a set age. People who say that it is at age 13 have a huge issue to deal with. What happens if the child dies at age 12 and 364 days? Is the child damned straight to hell?
I personally beleive what C.H. Spurgeon said. "If a child can knowingly sin, the child the can knowingly be saved." that is the age of accountability, when the child can knowingly sin.
The bible says that we must confess our sin and call upon the name of the lord to be saved. That we must believe in Jesus Christ to gain ever lasting life. (John 3:16) (Romans 10:13)
I also believe that God is merciful and that God is a righteous judge and that the opposite of what C.H. Spurgeon is true. I have no biblical evidence to back this up except that God is Merciful and just. THat if a person can't knowingly sin. then that person can't be saved, and is protected.
For example, MY family was friends with family that adopted and took care of special needs children. They had a daughter with Trisome 18. She was blind, deaf, and mute. She had no cognitive function past that of a 1 year old. I do not believe that she could understand what sin was, that she could sin, or who Jesus was. I believe that Christ will take care of her and bring her home. Since all life is precious in God's eyes, I can not see him damning her to hell simply because she is in capable of confessing Christ.
But those cases of people not understanding and not being able to confess are far and few between.
All this to say, This is why from the moment my child exits the womb and I can hold them and talk to them, they will know who Jesus is. They will know what sin is, and they have every opportunity to know Christ. For we brought nothing into this world and we can take nothing out, but i will try my hardest to make sure People go with me!