Sticking the tongue out can have many meanings. Children may use it as a sign of silliness, while people might do it to express disgust. A person may also stick their tongue out if they need to concentrate.
A baby who sticks their tongue out could be learning about their body, or it may indicate an underlying issue.
Some conditions have symptoms that can cause someone to stick their tongue out. These signs tend to accompany other symptoms, depending on the underlying issue.