My 2-year-old, next month 3-year-old daughter started being able to reach up to open doors a few months ago. I was happy for her.
For at least a week now, however, she has been going in a door first, then shutting or slamming it, and locking it right away. She does this with the bathroom door, her bedroom door, even the car door before she sits down in her carseat and I need to open the door to buckle her in. Today was the last straw though. She slammed the door while her brother's hand and toothbrush were in the bathroom doorway, hurting his arm, and locked it.
I've been telling her "no close door" and especially "no lock doors" for days but now I'm not sure if she knows what I mean. After I talked to her about and disciplined her for hurting her brother with the door, within a few minutes she had gone in her room and closed and locked her bedroom door. I had her open the door and I once again told her to leave the door open as I led her past the open door to her bed for her nap.
I realize that having a policy of keep the door open is not always wanted, such as when a guest is here and we want to close the bathroom door, but that doesn't happen too often.
If you've been through this, what helped you?