As a licensed speech language pathologist, I find your advice to forgo speech/language intervention disturbing. There are plenty of children who have NORMAL DEVELOPMENTAL errors in their speech. /s/ and /r/ were mentioned correctly as later developing spoken phonemes. Obviously, children with developmental "errors" are not in need of formal intervention/speech therapy. However, not all children will simply "grow out" of their speech problems, because their problems may be indicative of DISORDERED rather than DELAYED speech or language patterns. As with any developmental problem, early intervention is absolutely key in a child's progress. Often, problems with communication are the first indicators of larger underlying issues like autism or hearing impairment. If you have concerns about your child's speech or language development, it's best to consult a speech/language pathologist to determine if your child is developing normal communication skills!