I have these great little greenhouses with little peat circles for the seeds.My 3yo is loving the fact that every morning he can see how much his plants have grown. He is growing cucumbers and watermelon. We are also growing a pumpkin seed in the window because he wanted to see the roots grow too. Just put a seed is wet paper towels, and then in a quart ziploc bag, and tape it to a window and wait. it is really neat to see.
We are also taking date stamped pictures of all the seed trays we have to see what the germination periods are and how fast they come up.
As long as they get to play in the dirt and see something grow they are happy!!