According to NoahsDad.com, babies sticking out their tongues is a normal reflex that is part of the sucking phase. Usually, this phase disappears at around four to six months when it is time to start spoon feeding the baby.
Despite the fact that tongue protrusion is often a characteristic of a baby with down syndrome, doctors are unable to diagnose babies with down syndrome solely because they stick out their tongues. In most cases, babies stick out their tongues as they start to learn how to use their mouths correctly.
Other factors related to tongue protrusion include a baby having a larger than normal tongue or having a small mouth. If babies do a lot of mouth breathing, there is a good chance their tongues stick out during the early months of their lives.