Because seeds come in such a wide array of colors, sizes and textures, they are great for creating mosaics and collages. You may want to use a collection of seeds that are already mixed, maybe seeds leftover from another activity, like rain sticks. You could also take the time to open several containers of seeds and look at each type. Compare the seeds to the plants they grow into, as well as to each other. Either way, the variety of seeds gives a great opportunity to introduce a multitude of descriptive words, as well as the concept of comparing and contrasting.
To make the mosaics, you can take your pick of these two ways. The first is the standard Elmer’s glue method. I like to put the paper on an art tray to control the strays, and provide a jar lid of glue and a paintbrush to make it easier for the children to control how much glue they use and where it ends up. The children can apply the glue and then select their seeds from a nearby container and sprinkle them where they’d like.