What are the recommended Sharīʿah subjects and books to teach mosque students, taking into account their varying ages and the difficulty of dividing them into groups?

The questioner is thanked for his interest in teaching knowledge in mosques, as this is from the guidance of the righteous predecessors. As for the suitable books for this age group: one can rely on the textbooks approved by the Saudi Ministry of Education, due to their adherence to the authentic methodology, excellent presentation, simple style, and progressive approach. If these books are not available, one can benefit from the two books: (Usul al-Iman fi Daw' al-Kitab wa al-Sunnah) (Foundations of Faith in Light of the Qur'an and Sunnah) and (Al-Fiqh al-Muyassar fi Daw' al-Kitab wa al-Sunnah) (Simplified Jurisprudence in Light of the Qur'an and Sunnah).