3 years+
These structures leave children explore their vision and their creativity. I only demonstrated the technique insisting on the fact that a structure/building has to balance itself in order to stand up, otherwise it collapses. Then, I let them free to create their own balancing structures.
Put some butter beans in cold water in the evening and let them stay over night. The water has to cover the beans. You dont need to put them in the fridge, just let them on the table, somewhere. The next day, you will see how the butter beans have increased their size as they are full of water now and also they are a lot softer than a day before. You can prepare the experiment with children and ask them to compare hard butter beans with soft ones.
Then, you take toothpicks and start sticking them into the beans to create different structures. Some beans might split over night, you may choose not to use them, it doesn't matter. Once the structure is finished and you don't wanna add anything else, you let it dry. The beans will harden again and the toothpicks will remain stuck for a long time, couple of years if you wanna keep them.
Have fun!
