Apple Classroom not staying connected to every student in my classroom

iOS 16.3.1

7th Gen

Had all of my students' iPads locked at the beginning of class (Yes, I checked) 15 min later 3 or 4 of them were no longer locked. I did not unlock and I had the iPad controlling it with me the entire time. All but one are not tech savvy enough ( they are 6) to figure out turning the iPad off and then back on turns off the connection with Classroom.