I'm very sorry you went through this! I can easily understand how upsetting it would be!

My dad has an electric car and for the longest time he didn't know he could unlock his car from the inside without the car being on, his keys, etc. The locks just blend in with the door. I know when I get panicky I stop thinking rationally and don't notice things in front of me. (I don't think legally cars companies could get away with doors that don't unlock from the inside unless it's running because someone could get trapped inside during an electrical failure and there would be law suits out to the wa-zoo).

Also, when I was younger, if my parents were going into the gas station or a store and left me or my sister behind in the car, they instructed us to lock the car from the inside. Generally they left the keys in the car, but still made sure we locked it. Perhaps he thought he was trying to keep you and your daughter safe. Or heck, maybe he just wasn't thinking and locked the car out of habit.

I agree with the others, start carrying a key with you. Also, talk to you husband about what happened so he knows to be more careful next time.

I hope you feel better soon!