You probably have recall bias and children develop awareness of how other people perceive them and start to act according to this perception around ages 7-9. Younger children have a relative lack of this perception, conformity etc, therefore suffer less from the effects of social anxiety and its consequences. Do you think a 5 year old kid really cares about how others view them? Certainly not to the extent that we do as we get older. The likely scenario is you developed a stutter for whatever reason, which has become entrenched and exponentiated by social anxiety, which then feeds the vicious cycle.