Pronouncing the voiceless (soft) TH
Ask your child to hold up a mirror in front of them and tell them to bite their tongue as they blow air onto the mirror.
Practice with simple syllables such as voiceless (soft) /th/ followed with vowel sounds. You can make a game with the child that if they are fogging up and spit splattering the mirror, it probably means they are saying the sound correctly!
Print or draw a large F and a large TH on two separate pieces of paper. As you say the /f/ and /th/ phonemes aloud, have the child slap the corresponding piece of paper in front of them. You could even bring two bells or something that makes noise and have them ring the bell to the corresponding sound.
For a child having difficulty between voiced(hard) and voiceless(soft) /th/, do this same activity but with TH written on two pieces of paper, one that says “VOICE ON!” and one that says “VOICE OFF!”
If your child is having difficulty with /th/ and /f/ sounding numbers, use this same discrimination activity but with pictures of the numbers next to each other. (Numbers 3 and 4, or 13 and 14 for example).
Make a silly hat or use a silly hat lying around.
Tell your child that when they wear the hat, they are in the “Think Tank!”
Tell your child that when they are in the “think tank” they need to find as many /th/ words as possible.
Mix up flashcards with /th/ words and other words mixed in.
Have the child sort through the words and find all the /th/ words. After you have the /th/ cards, have the child say each word using the carrier phrase “I’m thinking of _____.”
If the card is “thorn,” the child would say “I’m thinking of a thorn!” Have them accentuate that voiceless (soft) /th/ for each word they say.
Stand in a circle (or if there are only two of you just stand across from each other).
One person throws the beanbag to another, saying “One Word Throw!” The person who catches the beanbag must use on voiceless (soft) /th/ word.
Then they say “One Word Throw!” and toss the beanbag back, and so on. You can extend the game by asking for 'Two Words Throw' or 'Three Words Throw'.
Have the flashcards or word list readily available so your child can think of the words quickly and you will get a lot of productions.