Holiday schedule nightmare starting early

Christmas is 4 months away and my ex is already making demands about having the kids from Dec 24-26 when the agreement says I get them the 25th. She's claiming "it's traditional" even though we've only been separated for 2 years.

Do I need to stick to what's written or try to work something out? I don't want the kids caught in the middle but I also don't want to set a precedent that the agreement is negotiable whenever she feels like it. What's everyone's approach to this?