Here is another educational kit that allows your kids to build multiple robots and learn a thing or two about programming in the process. The Makeblock MotionBlock Robot has over 10 forms. It can be programmed in Scratch and Python. You get a simple app to interact with the robot.
MotionBlock has high-performance smart servos with max torque of 25kg.cm. You can easily build a robot fighter, dog, and arm with this.