Those kids would only be judged on what they knew. I would think that most if not all made it to Heaven.
Really, how do you support this Biblically? Humans are born into sin, children are humans. Where does it say that ignorance is a get out of jail free card. Further, what makes you think that most children in third world countries have never heard of Jesus?
Well, do you really think that these children had heard of Jesus in any accountable way so as to make a decision? I would say that they knew no more of Jesus than we know of Buddha.
I’m asking you for Biblical support for your position. There have been large groups of people that have a large number of those children are damned. There’s a reason the Catholic Church baptizes children and the Mormon’s do after death baptisms.
In any accountable way? What exactly does that mean? By that definition, I’d say that no one alive has ever heard of Jesus in an accountable way.
Your assertion that you can choose not to follow Christ and then after death pick him is in my experience a very minority one.