After pondering Ben's mom's comment below, and my own annoyance, I have come up with a simple solution. Here it is, all you people who ever have occasion to make small talk with the parents of a baby or toddler. Instead of asking whether they have passed this or that developmental milestone, potentially annoying parents of a child who is taking his own time in some area, why not ask: "What does Baby like to do the best?"
Every baby, no matter how small, has preferences. The parents will be thrilled to talk about them. You might get a cute story out of the deal. You might have to listen to more than you want to, I suppose, but that's part of the perils of civilized conversation. Especially with new parents.