I lock my front door, as licensing requires this for safety of the children.
Parents are allowed to come over whenever they want, but as I explain to them, their child has already said goodbye in the morning and now has to say goodbye when they leave again. This usually turns into tears and causes the other children anxiety. So, the parents know if their child seems upset they have to take them with them.
When a parent comes over they cannot stay longer than 5-10 minutes, as they need to have a criminal record search to be present with the other children. This is required by our licensing regulations.
Good luck.