Little Kids in the Masjid?!

Shaikh Muḥammad Naṣir Al-Dīn Al-Albānī, may Allāh have mercy on him, said:

[The Prophet ﷺ] would not forbid them [from bringing their young children]; rather, he showed that he approved of this situation. In fact, he had even established a specific ruling to apply to it, taking into consideration the feeling of any mothers praying behind him ﷺ with their children crying at the same time: the Messenger ﷺ would pay attention to this, even while he was calling upon his Lord, that there was a woman praying with her child. So he would get started, as he said: “Indeed, I get started with the prayer intending to lengthen it, but then I hear the crying of a child and then shorten it, so that I can free his mother up to attend to him.”

[…] Then if something crops up from [a child brought to the mosque]—and there’s no way it cannot but crop up from him—of [behavior] that does not befit mosques like messing or playing around—and what kind of messing around do you want to take as greater than taking the Chief of Mankind [ﷺ] as a mount to be ridden upon? Yet despite that, he did not denounce it; rather, he established a specific ruling as well, just as he had done there with the mother of the [crying] child: he lengthened the prostration.

Silsilah Al-Hudá wa-l-Nūr, tape 668, as quoted by Jāmiʾ Al-Turāth Al-Albānī fī-l-Fiqh, vol. 8, pp. 69-72.