The mouth is... ...The major sensory organ for small children, and since food is close to the top of a very short list of needs that babies have, the question, "is it edible?", is a very important one to every baby. "is it fashionable to wear" and "does it have 4g" are questions that come up at a somewhat later age.
Exploring. Babies use all of their senses to explore their environment. Remember, your baby is encountering things for the first time. Babies use their mouths to explore new objects- it's a normal developmental stage- enjoy watching it. Just make sure that the objects they are putting in their mouth are safe! the link below is for choking prevention: http://www.Cpnonline.Org/crs/crs/pa_prevchok_hhg.Htm.