Consonants appear from front to back and vowels from back to front--and all this in just on semester!
Typically, the front consonants will be used first. The range of vowels will also be restricted, with the back vowels appearing first.
This could easily account, at least in part, for the fact that the names of close family members in many languages are words that start with front consonants and back vowel, as in "mama" and "papa" or even "dada."
Perhaps the most striking thing of all is the fact that the sounds the baby is making are now recognizable as being the sounds of the baby's language environment.
In just 6 short months, this speck of humanity, who has spent much of his/her time peeing and pooing, crying and cooing, has found time to secretly extract from the surrounding stream of vocal sounds, many of the allophones of the language!
That’s more than I accomplished in a year of Russian in college, with the exception of the pooing and peeing.