Why are unborn babies and those who are ignorant of Jesus get a free p to heaven?

There is an age of accountability. god is just and he knows babies and those who are mentally impaired can not understand or make a decision to accept him. That why the go to heaven if they die, "only those who believe in Jesus and accepts him as their savings goes to heaven" <=== This applies to people like use who can choose and are intelligent enough to know whats right and wrong and the requirement to be saved.