Give each person a square of tinfoil. Invite them to mould or shape something out of the tinfoil that is a symbol of their prayer e.g. an aspect of their life that they would like to offer to God.
Encourage them to pray silently as they create the shape.
You may like to have a small cross where they can leave their shape when they have finished praying. This works well as an activity as part of a series of worship stations or prayer spaces.
Alternatively you can use playdoh, or simply invite them to cut a shape out of paper.