Passover begins at sundown today and that reminds me of one of our family's fun memories involving a celebration of a Christianized version of Passover. All the proper foods were prepared and we each had a simplified script which gave an idea of what Jesus was doing at the Last Supper. We set a place for Elijah and hid some matzah and typically invited another family to celebrate with us.
I'd be in way over my head to give you advice about how to truly celebrate a Seder meal, but I am certain that knowing what Jesus did on His last days and remembering it in some way will make the event more meaningful to your family.
If you'd like a serious celebration, start with this impressive resource. If you'd like something simpler or for shorter attention spans, go to the library tomorrow and check out a picture book or two on the topic. You'll find there are many choices available. If you'd like to plan your dinner to support the fun, you may find some helpful suggestions here.
No matter how you mark the occasion, be sure to end by putting it in context of the New Covenant in Christ. The Catechism tells us that "By celebrating the Last Supper with his apostles in the course of the Passover meal, Jesus gave the Jewish Passover its definitive meaning." If you attend Mass on Holy Thursday (and you know the Church Ladies recommend you do), the readings will be about God establishing Passover as described in detail in the book of Exodus, and Christ's last celebration of it from the book of John. It's hard to find a better example of Saint Augustine's declaration that "the New Testament likes hidden in the Old and the Old Testament is unveiled in the New."
Image Credit: Francisco de Zurbaran, Agnus Dei