I have a friend who planned a 10 Makkos treasure hunt throughout the Seder she gave the kids clues to different locations and when they went there they found something connected to each of the makkos (ex. red jello for dam, little toy frogs, etc.)
Puppets are also great for them to act out parts of the story as you read through the Haggadah. You can buy coloring books of the Pesach story and let them color them while you are cleaning the week before and let them follow the story from their books (the haggadas from school usually go through simanay haseder, not the story of Yetzias Mitzrayim.)