There is nothing wrong with accepting a gift from a non-Muslim on Christmas and that is not regarded as participating in it or approving of it, rather it should be accepted as an act of kindness with the aim of softening his heart and calling him to Islam.

Muslims cannot celebrate Christmas because it is an imitation of the unbelievers. Also decorating Muslim houses with balloons at Christmas is obviously joining in with the unbelievers and celebrating their festival.

It is not permissible for the Muslims to attend the festivals of the polytheists, according to the consensus of the scholars. It is also prohibited to greet the non-Muslims on Christmas and other religious holidays.

It is not permissible for the Muslim to eat foods that the Jews, Christians and disbelievers make for their festivals. It is also not permissible to give them anything on the occasion of their festivals.

It is not permissible for any Muslim to join in the festivals of the non-Muslims, whether by attending the festivities or enabling them to hold their celebrations, or selling any goods or products that have to do with these festivals.

It is not permissible for the Muslim to join the non-Muslims in their festivals and to express joy and happiness on these occasions, or to take the day off work, whether the occasion is religious or secular.

The basic principle is that you should not accept any kind of gifts given on your birthday whether they are given to you on the same day or afterwards. Accepting birthday gifts implies approval of the occasion and helps to perpetuate it. So you should excuse yourself from accepting them, with the best of manners.