Don't just give your preschooler experiences with seeds in the spring.  Now is the perfect time to find LOTS of native seeds.  In your explorations to find seeds, preschoolers learn that seeds grow from plants, fall to the earth and survive the winter to germinate in the spring.  See if you can find a spot to harvest some seeds and save until the spring for planting.

Seeds Go, Seeds Grow by Mark Weakland is a beautiful non-fiction title. With big, clear photos of various kinds of seeds, seeds germinating and very brief informative text, it is an ideal choice for preschoolers to learn about seeds.