Is it permissible to buy sweets to celebrate what is called Christmas, in response to the parents' request, while only consuming the sweets and not participating in the celebration?

Buying and selling on the occasion of Christmas is forbidden because it is a form of cooperation in sin and aggression. The Permanent Committee for Scholarly Research and Ifta stated: "It is forbidden for a Muslim to assist in this holiday or any other forbidden holiday with anything, whether food, drink, selling, buying, manufacturing, gifting, corresponding, advertising, or anything else. This is because all of that falls under cooperation in sin and aggression and disobedience to Allah and His Messenger. Allah Almighty says: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression. And fear Allah; indeed, Allah is severe in penalty."

If it is established that this is an act of disobedience, then it is not permissible to obey one's parent in it, for the Prophet, peace and blessings be upon him, said: "There is no obedience in disobedience to Allah; obedience is only in what is good."

As for accepting gifts from them on their holiday, there is no harm in it. In "Iqtida’ As-Sirat Al-Mustaqim" by Sheikh al-Islam Ibn Taymiyyah, it is stated: "As for accepting gifts from them on their holiday, we have previously mentioned that Ali, may Allah be pleased with him, was presented with a gift on Nowruz, and he accepted it."

Ibn Abi Shaybah narrated from Aisha, may Allah be pleased with her, that she said: "As for what is slaughtered for that day, do not eat it, but eat from their trees."