Autumn time is nut-time - you need a nut-cracker!
Another project to build with kids. the cracker consists of easy to assemble components.
simply put the nut in the slot under the lever arm. Obviously all to do now is to bend down the arm.
There is a small stick to prevent a complete smash; depending on the nut you can choose the right length out of the magazine.
As the arm creates some strong pressure and force, the construction would tip to the front hence there is some area on the back, which you can hold and press down during cracking
The thickness of the parts is 14mm, the sink 35mm is around 2mm deep, the 10mm diameter for the stick has been drilled ~10mm. All measures are quite uncritical and can easily be adapted.