Question: how long does ice cream stay good?

I may have just poisoned my five-year-old son. He was entitled to dessert for finishing his dinner, and when I asked what he wanted he walked with authority to the freezer. After opening the door, he pointed to the farthest reaches of the frozen vegetables to a carton of frozen yogurt I forgot we even had. Apparently, his mind had recalled the tantalizing box of deep purple containing the flavor, black cherry. I have no idea when I bought this treat, but as I pulled it out, I coaxed him into accepting a possible alternative as I could not guarantee its freshness. I checked the bottom stamp and found it must be sold by June 2007. Feeling slightly better, I pulled open the lid to reveal just one serving missing from the carton, and a heavy layer of protective ice covering the luscious lactose. I grabbed an oversized spoon and peeled away the upper layers, took a taste of what lay beneath, nodded, and scooped him out a bowl. He gobbled it up, but I felt somehow, that I had done him wrong.