Here is a clever mechanical robot arm designed to keep your kids busy. The Thames & Kosmos Bionic Robotic Arm has a segmented arm that is driven by cables like tendons in muscles. This is a DIY kit and has about 300 plastic pieces for assembly. The arm has 360-degree movement with 23-inch horizontal and 15-inch vertical range. It has two joysticks for easy control.
This mechanical robot arm has two interchangeable end effectors, including a gripper claw and eel head. It requires no electricity or motors. You can find out more about it here.