Does sending one's children to schools whose curricula include the glorification of national and Christian holidays, and concepts such as democracy, secularism, and nationalism, alongside the teaching of the Holy Quran, render the one who does so an apostate? And what is the ruling on that given the unavailability of educational alternatives that qualify for higher education?

Merely studying in schools with curricula that contravene the doctrines and laws of Islam is not considered disbelief (kufr), unless it is accompanied by acceptance and approval of the disbelief within them, and a failure to repudiate it. As for the ruling on studying itself, in terms of permissibility and prohibition, the matter requires knowledge of the actual situation, the availability of alternatives, and the ultimate consequences. The question should be directed to the scholars in the questioner's country.