The church I go to has a separate area for Sunday school for the kids. The building is a big X with the church space at the bottom of the X and the Sunday school halls the top two spokes of the X. We haven’t left my granddaughter in the Sunday school area yet, but I know they have a great security system for drop off and pick up.
I don’t know how the Sunday school entry area is monitored during services (because I’m always in the services instead of the halls) or what they have in place to protect the kids. I have to chat with our security team to find out.