Aside from electrical outlets themselves, there really isn't anything.
The latest person to report seeing the ghost children has no electronic/electrical devices in the room at all, aside from the lights.
It cant be the in-room climate controlled heater/cooler units, since people in the oldest wing (which uses a radiator!) have also reported the ghost children.
Now, the whole building kinda does have janky outlets. People are just plain stupid, and lower the beds on the outlet covers and crush the bejezus out of them all the damn time. Because we never know what kind of resident (or their needs) will come through our doors when we have a vacancy, the rooms have quite a few outlets so that things like oxygen concentrators and the like can be plugged in. I would not be surprised if the wiring itself is leaking EMI all over the damn place.
Again, smartphones typically carry a magentometer inside them, as it is used against the earth's nascent magnetic field for deriving the bearing of the phone carrier for GPS navigation. It can also give useful raw magnetic environmental data, with the right application. If I were a douchebag, I would surreptitiously sideload such an app on everyone's phone.
I suppose I could just find
a suitable app and load it on my own phone, along with GPS tracking, and use it to get a picture of the magnetic anomalies in the building over time, since I too am all over the place. It would just take longer.