Is it permissible, Islamically, for the heirs to reclaim land that their mother donated to a mosque, under the pretext of "deception" in exchanging it for another piece of land, knowing that the exchange took place with the donor's full consent?

If a woman disposes of her land while she is healthy and of sound mind, then the exchange is legally valid, because a person has the freedom to dispose of their wealth, as long as it does not involve extravagance, wastefulness, or unlawful spending. This falls under the general command to spend in the way of Allah. Accordingly, the heirs do not have the right to reclaim the land. Even if the exchange took place during a death illness or while she was not of sound mind, the children's silence until the completion of the mosque construction nullifies their right to object, unless they have a valid excuse for this silence. The reference for such matters is the specialized Sharia (definition) courts.