IDEA: Kids deliver a speech on something important to them and others, while "standing at the gate."
A modern-day equivalent of the prophets might be speakers at Hyde Park London, Speakers' Corner. If you do an image search, the Internet has many interesting photos of the various individuals and groups who appear at this famous location. Some are political, some are environmental activists, others share religious beliefs. Some are just plain crazy! (Or are they?) The images will give your class a taste of the variety of speakers.
In much the same way, prophets stood at the gate of the town, or at the well, both popular meeting places. Sometimes several prophets met at the same time. I'm sure at times it was a noisy, passionate, even antagonistic occasion. Sometimes prophets disagreed with one another, and preached opposite messages. Some protested against the monarchy, others were sympathetic to ruling classes. The crowd had to discern for themselves what represented God's call to them.
One activity our youngsters enjoy is a game in which two speakers stand in fromt of the class and speak on topics they care about. It can be a hobby, a class at school, current events, their pet, something they are arguing with a sibling about at home, anything they wish to speak on. The catch is, the two speakers must speak at the same time! The goal is to see who can either attract the most interest (a vote from the audience) or have the audience remember most of their speech. The game is called "Fight for Your Attention" but you can rename it something to do with Prophets.
The first time, kids may be unsure how to proceed, but after a while, they start shouting (hope you have soundproofing!). This can lead to a good discussion about what is it that attracts people's attention? Is it the words? the volume? the clothes? the hand gestures? actions? singing?
Try having two speakers only allowed to whisper, or not speak at all. How do they get their message across?
In debriefing, you can explain that many prophets used "guerrilla theatre" techniques, employing drama and improv to attract a crowd or demonstrate their point. Think of Jeremiah and the broken pot, or Hosea marrying a prostitute. Isaiah and Hosea publicly named their children odd names (can you imagine going through life called "Unloved?") I bet Jonah attracted a crowd if he told his "swallowed by a fish" story! All these were memorable actions that emphasized their message.
Kids may learn that simply shouting isn't enough to make your point. What else is necessary? Passion, inspiration, eye contact, compassion, wisdom, all attract attention.
Then ask: how do you choose what to believe? on TV? radio? peers? adults? is it appearance or substance?
Anyone can stand up and claim to be a prophet, both in ancient Israel and today. But it takes a community of faith to determine the presence of God in the words.