According to Chicago Parent, the bubbles that babies blow are an essential part of early speech development. The bubbles are a result of mouth movements that occur while the baby is learning how to create various controlled sounds that later lead to actual speech.
The bubbles that a baby produces, along with blowing raspberries, are the baby's attempt to control sound volume from the mouth as well as to imitate the sounds others make around the baby when speaking. Bubble blowing typically begins at the ages of 6 to 8 months, with successful creation of the raspberry sound occurring more quickly if the sounds are demonstrated for the baby. The effort to teach the baby to recreate the sounds also helps babies learn the back and forth flow of normal communication as the child responds to sounds made by those around him.
Along with developing speech, the bubbles and raspberries a baby makes strengthen the jaw and the lips, aiding in eating solid foods and enabling the creation of an effective seal of the lips to prevent food and drink from falling out of the mouth. The back and forth flow between the baby and his parent or sibling who is teaching the baby to create the sounds also works as a bonding experience.