The affricate “ch” is a later developing sound that can be tricky for a lot of kids to figure out how to produce correctly because it’s actually two sounds in one– /t/ plus “sh.” There are so many different ways kids can misproduce this sound, ranging from having generally the right idea but with lateralized airflow release over the sides of the tongue, to moving the placement to the wrong part of the mouth altogether, or dropping off either the /t/ or the “sh” part.
Because it’s generally fairly easy to teach a good /t/ sound, I like to use the strength of this production to teach kids to make “ch.”
What you need: a child who can produce /t/, a tongue depressor if tactile cues are needed or a mirror if visual support for lip rounding would help
How to do it:
Tell the child to produce a /t/ sound. Praise them for the good sound.
Next, tell the child that you want them to hold out the /t/ sound to make “ts” (bonus step, you can use /t/ to elicit /s/ if the child is unable to complete this step). Have the child repeat “ts” a few times and praise them for it.
Next, instruct the child to make a “ts” with rounded lips. Have them say “oo” to feel their lips round and have them watch in the mirror if they’re struggling. Do 5 to 10 repetitions until the child is able to repeat “ts” with rounded lips easily.
After the child is able to produce /ts/ and round their lips, tell them “now we’re going to start the sound a little farther back in your mouth.” The target position for “ch” is to have the /t/ portion of the contact just behind the alveolar ridge, or the “drop off” behind your gums. Tell them to feel along the roof of their mouth with their tongue to feel how there’s an “edge” to the back part of their gums behind their teeth. A tongue depressor to give a tactile cue of where you want them to start the sound can help also. Once they know where you’re asking them to start the sound, model a “ts” with rounded lips, starting with contact in the post-alveolar ridge (i.e. palatal) placement. This will be a sustained “ch” sound. Have them repeat it a few times until it feels easy.
The final step is to shorten this long “ch” production by telling kids to do the same thing, but stop the sound sooner. Model “ch” and see if their imitation skills have improved. If so, great! If not, back track to an earlier step in the process and see if you can get better automaticity of a step they struggle with to have better success with the “ch” production.
Once they have an easy time producing “ch” in isolation, they’re ready for syllables. Start with mid and back vowels that are either lax or rounded to help ease into the transition from the new “ch” production to a vowel. For example, “choo,” “chah,” and “choh” will probably be easier than “chee.” So wait for high front vowels until they’ve got the production down for a few sessions!