All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad, sallallaahu 'alayhi wa sallam, is His slave and Messenger.
Firstly, we would like to underline that it is permissible to accept gifts from the disbelievers in Christmas or other festivals and occasions. Ibn Taymiyyah said in Iqtidhaa’ As-Siraat Al-Mustaqeem: “As for accepting their gifts on the day of their festival, we have previously mentioned that ‘Ali, may Allah be pleased with him, was given a gift on the (Zoroastrian) Nowruz Day, and he accepted it.” [End of Quote]
However, it is not obligatory under the Sharee‘ah to accept such gifts from them, and therefore, your husband has the right to refuse your mother’s gifts for his children. There is nothing wrong with supporting your husband’s stance and obeying him in this regard, especially since you have a valid reason, which is maintaining a good relationship with your husband. Moreover, you bear no sin for angering your mother by approving your husband’s stance. However, you should strive to please her to the best of your ability and invite her to visit your house or seek her acceptance that you visit her.
We also advise you to supplicate Allah, The Exalted, to guide her to the truth, and leave no stone unturned in helping her in this regard; this is one of the greatest manifestations of your dutifulness towards her. In addition, it is a very rewardable act; it was narrated on the authority of Sahl ibn Sa‘d As-Saa‘idi, may Allaah be pleased with him, that the Prophet said: “If one man is guided through you (to Allah), it would be better for you than having (a fortune of) red camels (a very expensive breed of camels considered the most valuable property in the sight of Arabs).” [Al-Bukhari and Muslim]
For more benefit on calling non-Muslims to Islam, please refer to Fataawa 84349, 91563, 21363, 30315 and 90486.
Allah knows best.