Along with the classic raffles, props, and candy, I always found that if the Baal HaSeider is excited, the children (who the Baal HaSeider has a Mitzvah to be there for ;-)) will mirror that excitement.
Additionally, a good friend of mine reenacts Pesach Mitzrayim at their Seider: they cover their doorpost in parchment paper and then spread tomato sauce on it, they sit with blankets draped like togas over their regular Yom Tov clothing, and parade around their table with their pillows over their shoulders during Avadim Hayinu and the actual Yetzia, with walking sticks in their hands of course...
If that's a little bit over-the-top for you (or if you don't have little children at home), then try using two intellectually probing Hagados: one for night one, and one for night two. Additionally, prepare for the Sidarim with those Hagados as well; I try to learn a little bit of commentary from my Hagada every night before going to sleep from Motzaei Shushan Purim until Leil HaSeider. Additionally, if you would like, I compiled a pamphlet of my personal Vertlach on the Hagada, accessible here: https://docs.google.com/document/d/1qijr6hTqjhEqoMtAvCu6hBJDs85XMgDVQii-sXckuTg/edit?usp=sharing
Hope that helps!