What is the ruling on children under the age of four or five being present during congregational prayers (Salat al-Fard) and disturbing the worshippers, and how did the Prophet pray while his grandchildren played around him?

Bringing children to the mosque was customary during the time of the Messenger of Allah, peace and blessings be upon him. Many hadiths attest to this, such as Al-Hasan (definition) climbing onto his back while he was prostrating, and his descending from the minbar to carry Al-Hasan and Al-Husayn. There are numerous benefits to bringing them, such as teaching them prayer and manners. However, fathers must supervise them so that they do not cause disturbance or tamper with mosque property; otherwise, it is not permissible to bring them.