YOU SAID:
Do they know it's christmas?
INTO JAPANESE
彼らはそれがクリスマスだと知っていますか?
BACK INTO ENGLISH
Do they know it is Christmas?
INTO JAPANESE
彼らはそれがクリスマスであることを知っていますか?
BACK INTO ENGLISH
Do they know it is Christmas?
That didn't even make that much sense in English.