On Facebook recently, I saw a woman fretting over the fact that her 22-month old daughter couldn’t pronounce the letter “L” in words like clock, cluck, flock, clear. She wanted to know whether she should look into getting the child into speech therapy.
I studied about half a degree’s worth of undergraduate psychology courses, and a full undergraduate degree of Russian language, as well as courses in phonetics and semantics. A child’s mouth is quite small, and the tongue is a comparatively large piece of flesh flopping more or less aimlessly around in that confined space. They’re learning motor skills at that age and only just starting to master gross motor skills. The movements of the tongue are fine-motor skills, so at this stage, a few mispronunciations and muddled sounds aren’t the end of the world.
In both adult and child language acquisition, the rule of thumb is that if you get the gist of what the person is saying, reward them, ignore little mistakes, and parrot back correct words and phonemes (sounds) (“Yes dear, that’s a flock of geese.”).
Having said that, catching serious speech anomalies in kids at an early stage is important, so it’s up to the parents and their physicians to make that judgment call.