We get a lot of questions on this website about delayed speech. Many of them come from parents of children under 2 years of age. To those parents I always suggest the importance of speaking clearly, reading little books and not pressuring the child to pronounce the words correctly. Creating anxiety in a child who has not fully mastered speech production is far more of a problem than having words mispronounced. I do not think any kind of special work-up is needed for a child younger than 3-years-old, as there is wide variability among children in the ages at which they acquire language skills.
However, since your son is almost 4, I would seek out a professional speech and language clinic and have him evaluated. At these facilities, highly trained individuals can determine the exact cause of your son’s problem and make recommendations about how to correct it. Among other things, they would examine all of his speech production organs (vocal chords and glottis, tongue, lips) and, in the process, find out if he is, as you fear, tongue-tied. That condition, which has a fancy medical name of ankyloglossia, is not very common. If present, it is fairly easily corrected by surgery. A good evaluation would not only determine the source of your son’s problem but would also provide suggestions of things you could do with him to facilitate better speech.
If there is no special speech and language clinic in your area, there may be a developmental center with a broader focus that could provide a full evaluation of your son’s development. Or there might be a speech pathologist in your community who works either independently or with a family practice physician or pediatrician. Whatever you do, try to be casual in your interactions with your son in order not to make talking an unpleasant activity for him. Respond when you can to whatever approximation of a word he produces. Don’t hesitate to say, “I didn’t understand what you said. Can you say it again and maybe point for me?” He will appreciate your acceptance of his efforts and undoubtedly improve with time.
Our parenting advice is given as suggestions only. We recommend you also consult your healthcare provider, and urge you to contact them immediately if your question is urgent or about a medical condition.