We do something similar for my sons' birthdays. We ask their friends not to bring gifts of toys etc, but to bring seeds. The children then have a great party planting the seeds and putting their names on the pots, when they visit they can see how they're getting on, and we send out photo bulletins on how the seedling race is getting on. Then when they all fruit, everyone joins in the harvest and the gifts just keep on giving. My children seem to love it.
Common Weeds And Wild Edibles Of The World (HD video)