Can I Have a Cup?

Setting: I am at the cash register during a rush at lunch hour today and there are many people both in the line and sitting at the tables...

Me: (I am waiting at the cash register waiting for some sandwiches to be made so that I can ring them up and a kid comes up to the cash register.)

Kid: (He is as cute as can be, a little boy who is barely reaching the top of the counter, about five years old.)
"Excuse me. Can I have a cup?"

Me: (I figure that the kid's parents asked him from a nearby table to get a cup for water because they are too lazy to get up.)
"Why sure!"
(I hand him a small cup used for water or small sodas)

Kid: "Thank you!"

Me: (I watch the kid take the cup over to the soda machine and fill it with ice and then some Dr.Pepper. He fills the cup all the way to the top. I continue to think that his parents are somewhere and they already paid. But then the kid goes back into the line looking pleased as punch towards another man.)

Kid: "Look what I got dad!"

Kid's Dad: "Where did you get that?!!" (Looking angry and confused)

Me: (Oops...)