Page "Limbo" Paragraph 36

In Islam, which denies the existence of Original Sin in totality, the concept of Limbo exists as Barzakh, the state which exists after death, prior to the day of resurrection.

During this period sinners are punished and the faithful rest in comfort.

The concept of underage children is that they go exempt of sin and that they are classed as Muslims and after death they go to heaven where they are cared for by Abraham.