Tell them as nicely as you can that they’re off base. Many children are not saying “mama” and “dada” at 9 months. True, some children are, but there is great variability in the age at which children begin to say words. Informal biography is full of examples of people who did right well intellectually—like Winston Churchill and Albert Einstein—who were slow in beginning to talk.
Without making a big deal out of it, make certain you talk to your daughter a great deal. If she makes any sort of recognizable sound, like “wrkt,” or “grf,” smile and say her little word back to her. Or say something else, perhaps something silly like “We’ll get some wrkt when we go to the store.” Talk to her as you go about your housework—“Mommy’s going to vacuum now.” She won’t understand the exact words, but she’ll get the idea that those sounds she hears are somehow important signals that have meanings she’ll figure out one day. Soon you can begin to show her pictures in magazines (“Look at the car”; “See the doggie”) and read short little books to her. My favorite baby book is Pat the Bunny, but you can find many excellent ones in any good book store or in the public library.
Our parenting advice is given as suggestions only. We recommend you also consult your healthcare provider, and urge you to contact them immediately if your question is urgent or about a medical condition.