What is the ruling on calling out to the deceased or a lost child, and what is the evidence for its impermissibility if that is the case, especially given the presence of the hadith: "Whoever calls out for his lost item, may Allah not return his lost item to him"?

If the intention behind announcing the death of a deceased person is merely to declare their death in the mosque, then simply informing people of their passing, without raising the voice, is not prohibited. Indeed, the Prophet, peace and blessings be upon him, announced the deaths of Zayd, Ja'far, and Ibn Rawahah to the Muslims. There is no harm in announcing the death of a deceased person in the mosque, but some scholars disliked raising the voice when doing so. Similarly, announcing a lost child in the mosque is not considered among the prohibited 'announcements of lost property.'