Most babies don’t lose the extrusion reflex—which makes them instinctively push out their tongue when anything other than liquid is placed in their mouth—until 3 to 4 months of age, and infant digestive systems are often not mature enough to process solid foods until after 4 months.
Before introducing solid food, your baby should be able to sit independently, hold up his head and be capable of transferring food from a spoon to his mouth. He should show interest in eating—by gazing at what’s on your plate, leaning in toward food or opening his mouth as if to eat. For most babies, this happens at some point between 4 and 6 months of age. But don’t rush it. “Waiting until your baby is good and ready will make the process easier for everyone,” says Stern. And contrary to folklore, adding solids will not make him more likely to sleep through the night.