When doing articulation therapy as a speech therapist, I believe the /th/ sound is the most difficult sound to help a child produce. Why is that?
In speech development, it is the last sound that is learned, usually around the age of 8.
Why is that?
Physically, getting one's tongue in and out for this sound requires cognitive focus and agility, so a second or third grader will have more success making this sound that a preschool child.
But there is another problem:
In Hebrew, there is no sound that is equivalent to the /th/ sound.
It is not heard.
It does not exist.
Children who learn Hebrew and speak in English, often will use an /f/, /d/,/t/, or /s/ as a substitute. Even if they could make the /th/ sound, they do not hear it, so they rarely use it. Parents are happy that their child is speaking English, why focus on this one sound?
It is true that when children learn to read in English, the /th/ sound is in the words, and they will learn to pronounce the sound correctly in reading, and later in speaking, if someone is there to correct them.
What can a parent do if the child does not say the sound correctly, ( as "da" for "the or "bafrobe" for "bathrobe")?
Both the child and the parents need to be motivated . If that is the case and the speech equipment ( tongue, teeth, lips and jaw), is in good working order, then the process should take only a few months.