I think the sensors are only for energy consumption on select power monitoring plugs. I think there is support for the motion sensors in the python-kasa GitHub repo but no support in the current integration or the tplink-smarthome-api GitHub repo.
I’m not sure on the exact flow of how the three components (TP-Link integration, tplink-smarthome-api, and python-kasa) interact but my best guess is motion sensors will be added by the end of this year, if it’s possible. The dev branch of core Home Assistant has also been updated to use the version of python-kasa that supports the sensors so it may be even sooner.
It would be awesome if they are able to add this since the Kasa motion sensors are significantly cheaper than the GE Enbrighten switches (at the cost of having to use WiFi and rely on TP-Link’s benevolence).
In the meantime, you can setup smart control in the Kasa app to use the motion sensor for turning on that specific light and have other devices be linked to that light’s state/transition for automations.