She's not defying the laws of physics. It's a tracked directional system that concentrates the ultrasound at the point of the device. Honestly, not even really that out there as far as the physics is concerned.

EDIT: Unlikely. Children hear better in upper ranges, not lower. And animals are unlikely to be too perturbed. These types of noises are generated naturally all the time.

The challenge here is the engineering. How precisely can you build the tracking? How much leakage is there? Are there problems with harmonics? How do you build an app that can relatively reliably 3d position a device relative to a base station. And finally, how do you get that base station to be able to simultaneously or rapidly re-aim itself to target each of the devices. That's hard, but certainly exciting and very possible.