A funny little encounter at the McDonald's

So I'm watching Foster and Grace at the McDonald's playplace on Friday night. And there are these two grandparents, also watching their grandkids in the playplace. They're probably in their mid to late 60s. The music being played in this McD's is something you'd find on a "Lite Rock" station. And Grandpa is singing, humming, or whistling along to whatever song happens to come on.