How to Deal With a Relationship Problem

My partner and I have been together for 11 years. He has two older kids, now adults, late 20s and early 30s. The thing is, his kids don't like me and won't accept me. They prefer they just have family, which equals their mom,. the two of them, and their dad, my partner. Now they've decided that this year, I'm not welcome at the family Christmas. Ouch. My partner is torn to not see his kids as hard, but he thinks this is just too much. Any thoughts or discussion or comments are welcome.