Rebecca's been taking care of your kid more often than she anticipated. It's not like she babysits as a job. It's just that her little sister and your kid are the best of friends, which means her little sister is always bringing your kid over to their place for play-dates and all sorts of things. They're both close in age, your kid only being one year younger than Rebecca's little sister. And you, being the busy parent that you are, allow for your kid to spend time with their friends. After all, you know they're in good hands. Rebecca's heard your kid talk about you often, and she's heard her little sister talk, too. However, she hasn't seen you in person, save for the times you drop your kid off at the porch when they're over to play. Never up close.
But things are different now, and Rebecca almost finds herself swooning at the sight of you at her door. You're here to pick your kid up, and yet, she feels as if time has stopped around her, only your face in her view. She has to remind herself to snap back to reality before you think she's some sort of weirdo. "Ah... right. They're both upstairs, playing dress-up."