You know, the thing that really ticked me off wasn't when you asked if my grandson and I were having a fun afternoon. While I don't think it's particularly exceptional, I know it is probably out of the ordinary for a 48-year old man to have a five-year old son. And there is certainly a ton of gray in my goatee and what there is of my hair. I wasn't pleased, mind you, but that isn't what really ticked me off. What really ticked me off is the fact that, after I icily said "He's my son" (and yes, it was icily) you didn't apologize and disappear. In fact, you stayed, without apology, and tried to engage us in conversation.
Now, I realize that McDonald's doesn't really pay you friendly grandmother types to sweep the floor. You're there to be friendly, to make sure the customers are enjoying their individual McDonaldland experience. So engaging people in conversation is your real job. However, an important component of that job is realizing that there are some people who do not want to be engaged in conversation, particularly after you've semi-insulted them. I'm personally content sharing my McDonaldland experience only with my son, thank you, and don't feel the need to discuss the weather or the meal or our day with a total stranger. That you weren't able to figure this out, even after I replied to your offer to get us anything else with a dismissive "No thanks, we don't need anything from you" (and yes, it was dismissive), that you still tried to engage us in conversation after that, would suggest that you aren't that good at your job. So next time we come in, think twice about coming up to engage us in conversation.