Here is another app controlled robot designed to get your young children curious about technology and robotics. The MeeperBOT 2.0 is LEGO compatible. It comes with an ABS plastic chassis, dual rear-wheel 300 RPM motors, and Bluetooth module.
The app gives you access to 3 modes. You can have the robot follow you via a Bluetooth leash. Kids learn how to program with BOTcode (via drag & drop commands). The MeeperBOT costs just over $50 at this time.