I get this question a lot. Just yesterday I was at a house and the mom asked me whether she should be concerned about her 3 year-old Eli’s speech. I asked about specific sounds, saying he should be able to say, t,d,p,b,m,n,w, but other sounds aren’t established until he is older, like s,l,r.
Often, parents are expecting too much of a preschooler–that he should be speaking perfectly and understood all of the time. The fact is, he isn’t expected to correctly produce all sounds yet and we shouldn’t correct him or call attention to the mispronunciations or he might feel like he isn’t a good communicator, and even start talking less.
In the case of Eli’s mom, she was noticing that he was mispronouncing sounds that she knew he could say. Mom said, “He says, nilk for milk, and I know he can say “m”. Sure enough, little Eli said he wanted more “nilk.” Sometimes kids hang on to random words that they have mispronounced since they were little and even though they are capable of saying those sounds, the word persists for a while. In this case, continue to affirm him with, “Yes, MMMilk.” Emphasize the mispronounced sound in your own speech. Later when you are brushing teeth or playing around, make some fun sounds and include the “m” with a few “milks” thrown in.
Never draw attention to these sounds that your preschooler can’t make. Maybe they are in a word as a blend which is much harder to say and will take a while for him to learn. If you are still concerned, find a speech language therapist through your school system, ASHA’s website or your pediatrician’s recommendations.