Myrna Shure: You are wise and thoughtful not to introduce anxiety to this boy’s parents. If speech is genuinely his only problem, and not the result of anxieties, speech therapy would be of value, and he is not too young. If there is, however, an underlying cause such as anxiety, it would be important to try to discover that cause, and perhaps by reducing the anxiety, the speech would take care of itself. It is even possible that his speech problem will outgrow itself with no intervention, as long as his parents as well as you stay calm, and not show any tension over this.
If the problem persists, you can get this child tested by contacting the local school system, office of special services/special education. In most states, they are obligated to test children to determine the need for speech therapy. Or, if needed, the boy’s pediatrician can test him, but I would discuss that calmly with his parents to see if they would favor that option.