SJS, probably a lot of people will disagree with me here–but I think that toddlers don’t need special instruction in Shabbos/ Yom Tov beyond singing songs, telling stories, and a simple art project or two. My 3-year-old learns about preparing for Shabbos by grocery shopping with me & watching/ helping me cook & bake. Of course we talk about what we are doing also.
Regarding learning about Yom Tov, I think that observing/ helping with Yom Tov preparations helps kids get excited & learn about what to expect.
If you are looking for fun worksheets or project ideas, a good source is http://www.chinuch.org (not sure if the mods will let this through, but it is under the auspices of Torah Umesorah).