Just keep hunting mushrooms until it rains again. You can pause, drop a child on a mushroom, unpause, drop another child on, and repeat again. Sorry but you're just going to have to wait for the rain to fall since you can't do a weather dance. Maybe switch to Slow speed while your villagers are starving. They eat less on that speed but will continue making tech points.
If they are really dying on you, you might want to pause the game, wait 24 hours and have the Chief make magic food. Keep doing this for a few days or a week or more. Have you already used the Chief to make magic food today? He/she makes it once every 24 hours.
