For starters, it’s creepy, Susan Katz Miller writes.
Your son is going to be excited about Santa, if only for a few years. And the way I see it, there’s nothing you can really do about this except to work to get comfortable with the idea.
Keep your mother company at her holidays. Your future kids can handle it.
Millennials are far more experienced and comfortable in relationships that cross traditional race, culture, and religious boundaries. And our culture is much more supportive of such families than it was. So you do have many advantages, heading into this marriage, over the interracial and interfaith couples from earlier generations.
Your question pushes us straight to the center of the tension between Judaism as an exclusive tribe with some inherited “birthright” component (with ongoing debates about patriliniality/matrilineality), and Judaism as a practice and belief system open to any and all.
You must honor their decision, or risk breaking up the relationship and having your daughter blame you for her unhappiness.
Being both Christian and Jewish spans a huge spectrum of beliefs and practices. Encourage your son to continue his exploration, and try to offset any external pressure he may feel to choose one religion, at this tender age.
Tell them. Tell them so that they can engage with the reality that many interfaith children, whether or not they were raised with Judaism, whether they have a mother or father (or grandparent) who was Jewish, want to be part of the Jewish community. Tell them, because demographically, a significant percentage of their clients, staff, and donors in the future will come from interfaith families. Tell them, so that they understand the ways in which you are an asset to their organization, because you provide an increasingly important perspective.
Six weeks is a very young relationship. Why don’t you give it the summer to see how your feelings unfold? As an emerging adult, you do not need to share every detail of your love life with your parents. Right now, you need private time and space to get to know each other, before you have to start defending your relationship to the outside world. If your love persists to Labor Day, it might be time to move ahead and include your families.
Your family is not a novelty. You are part of a growing movement to give interfaith children an interfaith education. But as pioneers in this movement, you will have to act as ambassadors, diplomats and educators in both of your communities. I suggest you offer to host a discussion group, inviting both communities, on what it means to raise children with both religions, and why you’re doing it.