A sparkling white wine.

You head to the kitchen to get Sarah's wine for her but when you open the refrigerator to get the bottle you put in there to chill, you notice it is gone. Your wife must have taken it with her to your parents. You curse beneath your breath and look for something else to give to Sarah. On the bottom shelf you spy a bottle of sparkling white wine that was given to you at work for achieving the highest total sales from the previous month. You select a pair of fluted champagne glasses from the glass cabinet and take them into the living room. You place a glass before Sarah and one for yourself and them release the cork with a loud pop.

"Oh champagne Mr. Doe!" Sarah says startled at the cork flying across the room.
"Its actual just a sparkling white wine. To be champagne it has to come the Champagne region in France," you explain.
"Oh," Sarah says dejectedly.
"It's really the same thing," you say with a conspiratorially smile to cheer her up.

You pour each of you a glass and after a couple more Sarah is giggling like crazy and lolling about on the couch. Looks like the bubbles have gone straight to her head just like you thought they would to a girl of Sarah's age.

Perhaps it is the loss of inhibitions that gives Sarah the courage to ask you, "you didn't ask me here to baby-sit, did you Mr. Doe?"
Your heart skips a double beat before you answer. "What makes you say that?"
"Durr. No kids," she replies.
You are unable to form an excuse after having been caught out like that.
Sarah however talks, with a slight slur now, before you can say anything. "So what was the real reason you called me over if it wasn't to look after the kids?"