Little girl lost

I'm struggling with the key in the mailbox, when I sense, rather than see or hear, a short figure breeze behind me.  A small girl comes up against the big glass door that fronts the building, and she reaches up and flips fruitlessly at the heavy handle to the latch.  She looks about four, can't be any older than five.

Without thinking it through, I walk over to open the door for her.  She doesn't acknowledge me, but rushes out on the path.  For one heart-stopping moment, I think she's going to barrel out into the street, but, after looking frantically both ways, she stops and sits down suddenly on the curb between two parked cars.

Silently berating myself, I walk out quickly but calmly.

"Are you looking for someone?"

"My mum told me to wait right here, and I don't know where she is!"

"Hmmn.  Well, you were in that building, so maybe that's a good place to wait for her.  There are chairs right by the door, so you can see her the minute she comes back."

To my relief, this seems reasonable to her.  We're just reaching the entrance, when a young woman appears, having run at high speed from the elevator up the hall.  

Her mother? An aunt? A friend of the family?  At any rate, my young friend evidently knows her.

"There you are!" the woman exclaims, and glancing at me, mouths "thank-you".

Well, she didn't know I let the little girl out.  I decide to head to our apartment, before she hears different.