What will happen to children who die at a very small age? Will there be a trial for them? If not (as I have heard), then would some people be allowed in Paradise without a trial?

Accountability in the Hereafter is based on the cognisance of good and evil. Human beings who have no appreciation of what is good and what is evil (like for example small children, mentally retarded or mad people) will of course be excused.

This is a common sense exception. We acknowledge it even today. Don’t our own courts excuse such people or in some cases treat them leniently?