>My kid went to a UC Berkeley adjacent pre-school and had researchers come by all the time, filming and taking notes (after consent forms were signed). They would share their studies with us later, it was very illuminating.

My undergrad had something similar. I took a class through it for some general credit. For one of our assignments we'd observe and take notes, sitting in the gallery space, which was a sort of catwalk above the classroom hidden behind a one way mirror. The whole classroom was microphoned and we could tune in to certain areas of the room to listen in. I am not sure if the preschoolers themselves were aware of the surveillance as probably that would influence their behavior.