The /th/ sound is a sound that you can see! Your tongue comes forward for this sound and you should be able to see it in the front. We make the /th/ sound by gently placing your tongue tip between your teeth and blowing, There are two /th/ sounds. One is voiceless (you do not use your voice) and one is voiced (you use your voice when making it).Most children can make the /th/ sound by the age of 6. Some errors of the /d/ sound for the /th/ and the /f/ sound for the /th/ can be considered dialect in our areas. It depends on the family and culture.