My Little Larcenist, I Mean Mia

Faith and Mia had been invited over to play at a friends house one morning and while I got ready to drop them off Mia entered the bathroom...

Mia: "Don't worry Mom, I have a key."

Me: "A key to what?"

Mia holds up a barrette: "A key to their house"

Should I be concerned, or is it normal for a 3-year-old to think she can pick a neighbors lock and walk in without knocking?