Are many sins committed in childhood forgiven after repentance and 'Umrah?

No matter how great the sin, Allah's forgiveness is greater. Allah forgives sins for whoever repents with a sincere repentance that fulfills its conditions: abandoning the sin, resolving not to return to it, feeling remorse for having committed it, and if the right belongs to a human being, then it must be returned or their forgiveness sought. Allah Almighty said: "Say, 'O My servants who have transgressed against themselves [by sinning], do not despair of the mercy of Allah. Indeed, Allah forgives all sins. Indeed, it is He who is the Forgiving, the Merciful.'" As for sins committed before puberty, there is no accountability for them, and for what was committed thereafter, repentance suffices.