Is it permissible to take the financial allowance for a child born in a European country after returning and settling in an Arab country without the government's knowledge, and is that considered deception? And if it is unlawful, must the government be informed or the money be given in charity, and what do we do with the money received if we cannot return it?

A Muslim is the most truthful of people and the most faithful to covenants and contracts. If you took a sum of money with a condition, then once that condition ceases to exist, you no longer have a right to that money, and it must be returned to its rightful owners. If you are unable to do so, then spend it on the poor and needy. You must inform the entity that you have returned to your country permanently; otherwise, this would be deception and a lie.