Many churches have All-Age Eucharists at their Harvest Festivals. We'll be trying the following idea at ours:
Before the service, pieces of paper shaped like seeds, along with pens and markers, will be placed in all the pews. At the end of the intercessions (which will be written and read by the children), the congregation will be given time to write or draw a prayer of their own on their seed-shaped piece of paper. During the Offertory, the seed prayers will be collected and brought to the front. They will be blessed, and the President will pray that these seeds of ours will "grow and bear fruit."
I'm not sure exactly where they'll go - whether they'll be planted in the church garden, and decay, and provide nutrition for the soil and the living things - or whether they'll be added somehow to the displays of wheat and fruit that adorn the Harvest altar, or some third option I haven't thought of yet. If you have any ideas for this part, let me know!