As for your son—first the disclaimer: without an evaluation, I cannot tell you specifically what is happening. I can give you general education though! Hope you find it helpful.
Please know that not all non-fluent speech develops into stuttering behavior. For some reason we do not understand, boys (more often than girls) can go through a rough period during the late toddler and early preschool years during which they have what’s called “normal non-fluency”. This usually appears out of the blue and can get worse and better, then worse again; and it can be quite alarming to parents. The duration is usually only a few months, but can be up to a year or so. Normal non-fluency resolves on it’s own and is best handled by NOT calling attention to it. That means getting grandparents, teachers, etc. on board to educate them.
My best advice (having not evaluated your child) is for you to follow your gut. If you have unanswered questions, do consider a professional evaluation —the evaluation will be worth the price of “admission” because it will specifically answer your questions of what to do or not do.
To educate yourself about stuttering, check out the Stuttering Foundation of America website. The link can be found on my webpage www.sandiegospeechtherapy.com. You can also find information on www.asha.org.
In the meantime, see if your son is “blocking”. Does his face or lips freeze during the pronunciation of letters at the beginning or in the middle of a word? Normal non-fluency typically includes sound repetition “I w-w-w-w-w-want some milk” or syllable repetition “I wa-wa-wa-want some milk” or even word or phrase repetition “I want…I want…I want..I want some milk”. Blocking is when the sound “freezes” and there is a period of time where nothing is coming out his mouth. Also, eye blinking, other distracting facial or body movements should be noted. If he is unaware of it and not frustrated, please do not call attention to it.
If you note blocking, or your son is frustrated with his own speech, these are one more reason to seek a professional evaluation. The incidence for stuttering is generally regarded as 1% to 5% of the population.
A speech/language evaluation can be completed as early as infancy, so it is not too early for an evaluation. Most experts believe that early intervention is best for children.
I hope you have found this helpful. Please do not hesitate to contact me for any support.