Thames & Kosmos Robotics: Smart Machines Science Kit

Amazon.com Price: $82.66 (as of 15/12/2019 09:32 PST- Details)

This kit gives kids a simple, fun, and customizable introduction to robotics that lets them build eight motorized machines.
Requires a tablet or smartphone
Using the app interface, you can program the robots you build to behave based on the feedback coming from the ultrasound sensor.