1. When your child gets about 3+ years old, teach them how to lock/unlock the door. Their fingers and hands should be strong and skillful enough now to learn how to turn a key. Reason for this is not so they can flee like a refugee, but rather for emergency cases like you pengsan (faint) and they need to let the paramedics in :)
2. When they can open the door:
- tell them when they are allowed to open it and to whom and for what.
- teach them to close and lock it at all times (you'll hear yourself repeating this for a few years). Children are so innocent that they don't know how evil lurks out there. I keep reminding my children how open doors may just be an open invitation to unwelcome visitors. I tell them about the knives or guns these people might have and their intention to steal things or to harm us. Not that I want to scare them (well... maybe a little) but they need to learn that there are consequences to their actions.