M.M.
I grew up in a mostly Orthodox house. My father was very strict about everything and Passover was definitely a difficult holiday for us kids. I am very much less strict with my own family. I actually don't make my son adhere to Passover. He is 10.
At 2 1/2, I would give him everything to try, but wouldn't hold him to rigidly to the holiday. Of course, it would be a problem to keep the house free of chametz. I did find some recipes for a Passover-friendly mac and cheese, but I wasn't sure they sounded so good. lol
Does he like matzoh? Spread it with peanut butter or cream cheese and jam. I eat that all year round. Matzoh brie might work. There are a lot of cookbooks for Passover that could help and tons of information online as well.
This could be a chance for him to expand his food horizon too. Maybe you can try recipes in small batches, ones that include a few known favorite foods that are Passover friendly, and see if he likes the variation? Also, look at the different traditions between Sephardic and Ashkenazic Jews. There a many rich delicious foods in both.