Maybe I'm just being cranky but personally it drives me crazy. While I do have terrific parents this IS my home and I need for there to be a boundary. To me just walking in is a sign of lack of respect. It's different if the parents have been told that they're welcome to just come in but to just do it is something else. I lock my front door for a few reasons but then again we're always on the main level during drop offs and pick ups. I ask the parents to call ahead if they need an early pick up so we can be prepared.