As your child gradually learns how to turn his thoughts into intelligible sounds, he's bound to make mistakes. These missteps are completely normal and your child will outgrow them on his own. You may notice it more when your child is tired, excited, or upset. He may also open his mouth to say something, but get stuck before any sound comes out.
Nobody knows what causes stuttering.
Many researchers think that small glitches in a child's brain may interfere with the timing and rhythm of his speech. Just as some kids have trouble catching fly balls, some simply don't have the verbal coordination to speak clearly. Stuttering can run in families, and it's four times more common in boys than in girls. The condition has nothing to do with intelligence, and it's definitely not a sign of bad parenting or hidden psychological problems. Stressful events such as moving to a new house or going to a new daycare can make stuttering worse, but they don't cause the problem in the first place.